3e - my 1st level wizard, with 12.5 gp (I.e. starting gold) can make a scroll.
First, it's 25 gold. 1(spell level) x 1(caster level) x 25gp. Second, it cost a negligible amount of XP for that 1st level scroll, so he couldn't do it with just starting gold and the feat. He'd have to earn some XP.
3e - my 5th level wizard can make any miscellaneous magic item with a negligible cost.
That's wrong. You have to be able to cast the spells required to make the wondrous item and at 5th level, that means a whole lot of magic items are out of reach. And again, you're paying XP to do it. Let's say you wanted to make a Carpet of Flying. Even though you can cast fly, you still need to be 10th level. So that's right out. Hold on while I look for one of the few items you can actually make at 5th level.
Okay. An Amulet of Mighty Fists+1(because you aren't high enough for +2). That's 3000 gold in materials, which is a whole lot of a 5th level wizard's funds, if he even has that much. It also costs 6000 gold for XP calculation, so he loses 240xp.
In 1e where you got a crapton more gold to spend on the items you are making, that's all it really cost. You wouldn't make items unless you had Wish to get the con back if you actually lost any. So time and money. No XP cost at all. If a 1e wizard learned how to make a Ring of X-Ray Vision, he could churn out 100 of them if he had the money, and he would since he could sell them.
100 Rings of X-Ray Vision would cost the 3e wizard 100k XP, in addition to the 1,250,000 gold. That would take a 15th level wizard down to 3rd level, except he'd stop being able to make those rings when he ceased being able to cast True Sight. Now he could use scrolls for that spell and keep trying until he drops to 5th level, but that involves yet more cost to buy or make the scrolls, and has a failure rate.
AD&D - My 11th level MU can maybe make a magic item, possibly at a cost of point of Constitution. The gp cost of making the item is unknown. I can get the Con back if I'm an 18th level wizard.
Yes, these things are the same.
You can't make a magic item with any chance of losing a point of constitution at 11th level. Permanency is what might cost the point, and that's an 8th level spell. Plus you could just get the con point back with a Wish spell. You wouldn't be making items until you could cast Wish.