Iconic wizard (int 15 at 1st level), and at 4th level mage with Int 16, +3 Int and 7 ranks in spellcraft, +2 snergy from Kno (arcana) = +12 spellcraft.
Remember its only;
15+spell level to learn a spell from a spellbook or scroll (no retry until next rank in spellcraft)
15+spell level to prepare a spell from a borrowed spellbook (one try per day, no retry)
Unless I am mistaken, the wizard can also take 10 (not take 20 as there are consequences for failure), by just taking 10, that makes it an easy 22 at level 4th... I dont' see a problem then preparing spells from another wizard's spell book. By 4th level you or the party should have its first bag of holding, to hold any captured spell books. During interlude's copy select spells into your personal spellbooks. By10th level I had numerous spellbooks, usually sorted by spell level, I use the 100 page limit for books.
The costs seem ok IMV, its not like the wizard buys armor or weapons. He does seek and will likely purchase any Int and/or Con items, but so does the fighter and other classes for their primary stats They all compete for general wondrous items. And if the wizard is crafting scrolls and potions, I would expect the party to contribute all the gold pieces, since the wizard is contributing the xp. Furthermore in the current game we play, we help the wizard acquire spells, generally if he needs a spell (knock, planar gate, etc.) the party contributes the gold for the scroll, the wizard covers the scribing cost.
Time restrictions sound strange, practically all campaigns I have played in over the last 20+ years have had long interlude, long travel time, resting, studying and training for the next level, crafting items (mundane or magical), waiting and searching for the next quest/adventure to embark on... The critical time sensitive mission are still there and fun, but they are not the norm.