Lock Please

[Nettlekid]

Forget about this, unnecessary.

[Emperor Tippy]

Shapechange into a Zodar and then use your free Wish's to Wish up a Blessed Book with all of the spells that you want in it. As it is a magic item its legal and then you just master the spellbook (instructions on page 140 of Complete Arcane).

That takes a week plus one day per spell.

[DevilsAttorney]

Shapechange into a Zodar and then use your free Wish's to Wish up a Blessed Book with all of the spells that you want in it. As it is a magic item its legal and then you just master the spellbook (instructions on page 140 of Complete Arcane).

That takes a week plus one day per spell.

Well that works... Except by the time you have that spell, it's pretty much pointless to want to save that money anyway!

[Story]

The most cost efficient way for Wizards to transfer spells barring high level shenanigans is to use the copying a Spellbook rule to make a copy at half price, and then give the copy to the recipient who masters it using the already mentioned Mastering a Foreign Spellbook rules.

If you're transferring a large number of spells at once, a Blessed Book or Auran's Spellshard (essentially a half price Blessed Book) might be cheaper.

A Geometer 2 can do things cheaper, but those are presumably rare. A large established Wizard guild will likely have a Geometer to do all their scribing for them, but it won't be plausible for your average hedge wizard.

[jiriku]

The Collegiate Wizard feat doubles the number of free spells you get at each level. That's pretty nice.

Use item creation feats to do everything for cheap.
If you're a fan of Vecna, you'll have enough cash by around 5th or 6th level to take the Sanctify Relic feat and craft a tome of the stilled tongue. Using only its entry-level power, it's basically a half-size boccob's blessed book. Getting that at an early level will really save you money in scribing spells. You can retrain the Sanctify Relic feat when you level up.
A lot of wizard spells are also on the lists of full-list casters who will automatically have access to them. Since you have Scribe Scroll, pair up with party members or NPCs who know spells that you don't and have them provide the spell while you scribe the scroll, cutting your gp cost in half. You can use a quill of scribing or dedicated wright homunculus to minimize the time you have to invest in scribing, so you can spend less time making scrolls and more time copying them into your tome.

If your game is high-op, then you can call upon the Tome of Extreme Cheese: ignore the previous relic and make a tome of ancient lore. This contains every spell in the game (for reals), and allows you to prepare one spell per day that you do not know. Protip: you can scribe a prepared spell into your spellbook. Depending on your tolerance for cheese, this can be used in conjunction with certain other tools to learn and cast any non-epic wizard spell by the time you hit 10th level.