Ancestral Relic would be a fun way to do it. Just make the item be your spell book.
JaronK
I feel your pain JaronK, I post that trick on every archivist build thread and no one notices it then either. If you are a good character, this feat by far is the best. It lets you sacrific anything with a listed gold value to increase the value of your choosen item on a 1:1 basis. It does not specify the effects have to be magical enchantments and you do not need any requirements to add whatever you want. It works just as well as mercantile background, at least for the spell book.
Mercantile sell at 75% buy at 75%
Ancestral Relic Sacrifce at 100% to get 100%
While you cannot sell at 75% to buy other stuff, you also get the ability to destroy items that are evil you would not want to sell, have a sink that lets you dump things of value without effecting the market (wall of salt produces 10,000's of gp), and can have alot of fun with a lich's phalactery.
Only Caveat, you have to be good.
To add to the geomancer fun, I like to add in the feat Arcane Shorthand from dragon #358. It cuts the space and price to scribe spells into a spell book in half. This is alot more fun with an archivist which can literally cast any spell when you take into account alternative spell source.
As for the domain trick, there is the feat Customize Domain from dragon 325 that lets you rearrange the spells on the domain. If retraining is allowed, you can take that feat and retrain it later.
One spell you might want to look at is "Choose Destiny", a level 9 spell in the Destiny domain from races of destiny. It does not appear on any other lists, but lets you roll twice for every action and take the better roll. Very funny as a persistent spell if you use divine metamagic tricks (or arcane divine metamagic tricks).