Dr. Awkward said:
Sure. Sorcerers can spend a fortune on buying all the scrolls they like. But wizards get them for half price based on a class ability. I never said that sorcerers shouldn't/couldn't buy scrolls. They should...at least until they can get hold of staves, which are generally superior. But it's much more expensive for them to do so.
Wizards have a class ability that lets them get the most out of their large spell repertoire by having backup spells for cheap. This is not something to be ignored.
It is obvious that you haven't actually looked at the math and hence the reason you mistakenly view it the way you do.
After first level, Wizards get two spells per level. All of other spells have to be either purchased or found.
If a Wizard purchases a spell, how much does it cost?
Well minimally, it costs the same as a scroll of that spell (25 GP * spell level * minimum caster level). Or, it could alternatively cost 50 GP times spell level as per page 179 of the PHB. This latter method of payment seems odd though since starting at third level spells, an NPC Wizard could make a lot more money selling scrolls than letting someone copy out of his book for the same level spell (yet another area where the economics in the game is broken). But in either case, it costs money to acquire the spell.
It then costs money to put the spell in his spellbook (100 GP * spell level).
So for each spell at each spell level a Wizard purchases beyond his two automatically gained per level, it minimally costs:
1, 25 GP (via scroll) + 100 GP = 125 GP
2, 100 GP (via NPC) + 200 GP = 300 GP
3, 150 GP (via NPC) + 300 GP = 450 GP
4, 600 GP
5, 750 GP
6, 900 GP
7, 1050 GP
8, 1200 GP
9, 1350 GP
Each scroll for the Wizard costs (assuming no expensive material components):
1, 12.5 GP
2, 75 GP
3, 187.5 GP
4, 350 GP
5, 562.5 GP
6, 825 GP
7, 1137.5 GP
8, 1500 GP
9, 1912.5 GP
Each scroll for the Sorcerer costs (again assuming no expensive material components):
1, 25 GP
2, 150 GP
3, 375 GP
4, 700 GP
5, 1125 GP
6, 1650 GP
7, 2275 GP
8, 3000 GP
9, 3825 GP
Now, it is a safe assumption that the Wizard will most often pick his free spells as ones which he will study a lot and more rarely make scrolls of those. He would more often make and use scrolls of his lesser studied spells that he acquires in other ways. The very first scroll that he ever makes if he purchases the spell (as opposed to finding it) at each spell level costs:
1, 137.5 GP
2, 375 GP
3, 637.5 GP
4, 950 GP
5, 1312.5 GP
6, 1725 GP
7, 2187.5 GP
8, 2700 GP
9, 3262.5 GP
It costs even more if the DM forces the Wizard to buy a scroll of the given spell. In that case, he would have to scribe the spell twice, just to break even with what it costs the Sorcerer to purchase the scroll twice. And, he would have to do this for every single spell he purchases, even those he rarely would scribe into scrolls.
As can be seen above, it isn't until 7th level scrolls that it costs the Wizard less to scribe his first scroll than it does the Sorcerer to purchase his first scroll of the same level.
Now, what happens if he finds the spell on a scroll or a spellbook. On the surface, it would appear that this is where he starts saving money over the Sorcerer.
Well, not usually.
There are several factors here:
1) If the Wizard finds the spell on a scroll, he has to expend the scroll in order to put it into his spellbook. So, it costs him 100 GP * spell level to get it into his spellbook. As an example, the Wizard is -300 GP in this case and has zero scroll whereas the Sorcerer is 0 GP and has one scroll. The Wizard would then have to scribe four scrolls, and the Sorcerer would have to purchase three in order for both of them to have four scrolls and the Wizard to pay less money (1050 GP vs. 1125 GP). If the Wizard scribes fewer than four 3rd level scrolls, the advantage in savings goes to the Sorcerer (and this applies to every 3rd level scroll found which the Wizard did not have in his repetoire).
2) If the Wizard finds a new spell in a spellbook, he again has to spell 100 GP * spell level to get it into his spellbook. He again is behind the eight ball in expenses before he even starts.
Now, what does a Wizard do with those spellbooks he finds. Well, he could sell some of them, but so would the Sorcerer. No advantage in cash for the Wizard there.
However, he would keep SOME of the spellbooks he finds in order to have caches of spellbooks where he could replace his own spellbooks if they get lost or destroyed.
And this is a MAJOR factor that you are totally forgetting and why the scroll GP math is really in the advantage of the Sorcerer.
The Sorcerer will sell every book he finds. The Wizard (if he is truly being played intelligently) will only sell books where most or all of the spells are duplicated in other books that he owns. If a given book has multiple unique spells that are not in any of his other books, it is STUPID for him to sell that book.
It is better for the Wizard to keep those books unless it is only a few spells where it is more advantageous to copy those spells into a set of spare spell books (which again costs 100 GP * spell level a SECOND time) and then sell the book.
And at a certain level, it is better for both the Wizard and the Sorcerer to craft/buy/find wands and then staffs, and scrolls start becoming less significant anyway.
So, what is the bottom line?
Wizard spends:
100 GP * spell level to put a new spell into his books
100 GP * spell level to put a new spell into a backup book
100 GP * spell level to purchase a new spell
25 GP * spell level * caster level / 2 to scribe a scroll PLUS spell level * caster level XP
Wizard acquires:
50 GP * each spell level in books he sells, but he does not sell all of the books
Sorcerer spends:
25 GP * spell level * caster level to purchase a scroll
Sorcerer acquires:
50 GP * each spell level in books he sells, but he sells every book he finds
A single found spellbook can buy a Sorcerer dozens of scrolls whereas the Wizard might not even break even by placing the new spells in his books, scribing the same number of same level scrolls, and then selling the book. This assumes it is a book he wants to sell. He will probably not want to sell a book that has a lot of new spells in it.
Now, it doesn't take an advanced Economics degree to see that in a normal game, the Wizard is spending boatloads more GP in order to scribe his stash of scrolls and maintain his spellbook and spare spellbooks, than the Sorcerer is purchasing his stash of scrolls.
So my point stands. It generally costs less for the Sorcerer to purchase scrolls than it does the Wizard to both scribe scrolls AND maintain his spellbooks.
Your theory about it costing the Sorcerer more for scrolls is flawed and misleading, and doesn't look at the big picture. Your point about Wizards backing up their lack of flexibility by scribing scrolls is basically moot to the discussion since Sorcerers can do the exact same thing and in the long run, it costs Sorcerers less GP to do so.
Advantage: Sorcerers (yet again)