As basic guidelines:

Staying at an Inn is assumed to be paid for by odd jobs and random income your character might have. As are all meals/drinks in said Inn.
A home is the slums is free, simply find a shack where the previous occupants are deceased and enjoy.
A home in the green area of Avalon is small in size, two or three rooms only, and costs 10,000 gold
A home in the yellow section is larger, 4-10 rooms, and costs 20,000 gold
A mansion in the red section is extravagant with servant quarters that rival the other homes and large plots of land surrounding. These cost 100,000 gold and more, speak with an admin about specifics.

Please bring all housing purchasing requests to an Admin via a pm on the Wikia or IRC.

Also please note that this is just for Avalon City housing. For building outside of Avalon City, and for fleshing out details, please make use of the rules found in the Stronghold Builder's Companion. If you do not have access to this manual, but want to know information contained in it, please ask about it on the IRC.