edit: I haven't found the GP costs to be trivial - probably because I have a hard time finding NPCs willing to let me copy spells.
That's what spells like charm person and dominate person are for. Beguile him, then copy the spell into your Blessed Book for free (only cost is time).
Alternatively, simply kill him and take his spellbook, then copy his spellbook for free.
Alternatively, kill him and raise him with Animate Dread Warrior (UE) so that he is still a (slightly gimped) wizard completely under your control. Then copy his spellbook for free.
Alternatively, kill him and perform the Ritual of Crucimigration on him and turn him into a Necropolitan (LM) so that he is a necropolitan and then rebuke/control undead. Now you have a fully functioning wizard mostly under your control. Then copy his spellbook for free.
Alternatively, cast Mindrape (BoVD) on him first, changing his memories to be your lifelong, faithful servant. Then copy his spellbook for free. Killing him and raising him as an undead is optional.
Alternatively, purchase a power stone of Mind Seed (EPH) and cast it on him and wait a week. Now he is you - 8 HD. Now cast Mindrape on him, then copy his spellbook for free. Killing him (yourself?) and raising him (yourself?) is optional.
Alternatively, use Mindseed, and then Polymorph any Object (possibly >1 casting) into some useful form- I suggest a symbiont from ECS or FF. Then Mindrape him and copy his spellbook for free. Then have him respec his spells to be a dedicated counterspeller, readying an action to counterspell any spell cast by you every round. Killing him and raising him is still optional.
Finally, my personal favorite, reserved for my favored enemies:
Mind Seed, Mindrape, Flesh to Stone, Shrink Item, Fine-sized Bane (creature's type) Shuriken, Sovereign Glue, and Wand Bracelet (MiC).
Mind seed and Mindrape as normal... use flesh to stone on him, follwed by shrink item. Make him the size of a charm for your Wand Bracelet. Then affix the shuriken keyed to his creature type to his forehead, chest, and hands with Sovereign Glue. Then attach him to your wand bracelet and pretend to be a barbarian that wears the corpses of his enemies.... with style.
Are you sensing a trend here that somehow the other wizard's feelings and reservations about sharing his spells freely are irrelevant? A DM's biggest worry about wizards should not be about what loot or spells he hands the wizard... but what monsters and characters he puts under their control by sending them his way.
Also, as an afterthought... if you play core-only, you shouldn't worry about wizards at all. You should worry about Druids... they fit all the roles (tank, healbitch, skill monkey, face/fop, adamantine cannon, and GOD) by themselves... and get 1.5x a fighter as a class feature. Note that non-Kobold Sorcerers are only comparable to wizards in core. Outside of core, their slow spell progression, lack of effective metamagic capabilities without hefty investment, coupled with the fact that a lot of unique sorcerer traits (the spontaneous casting, the sorcerer-only spells, etc.) are replicated entirely by feats or other class features, such as Spontaneous Divination (CC), Shadowcraft Mage (RoS), and Uncanny Forethought (Elder Evils), without sacrificing the versatility and INT-synergy (stronger stat than CHA, imo) of the Wizard, makes Sorcerers vastly outclassed by the Big Five (wizards, clerics, druids, artificers, and Spell-to-Power Erudites).