The price of a house depends on the city.
The cheapest is the one in Whiterun, but requires you to do some of the starting main quests in Whiterun.
This costs around 5k to buy the house and around 2k to decorate.
The next cheapest is in Riften. There you need to do the Skooma Side Quest (speak to the Argonian in the docks - fishery I think) as well as help 5 people which misc quests. Once done you will be able to purchase a house for around 8k and about 5k or so (maybe less) to decorate.
The most expensive is in Solitude I think. Costs 25k to purchase (have to do 5 misc quests and the Wolf Cave quest, received when you go to the Jarl's palace). It costs around 11k to decorate.
Lol, I never actually felt the need to buy houses in other towns as I do most of my stuff in Whiterun and being a werewolf I don't really need to sleep so I assumed they were all 5k.
Doh! That is where they went!All I'll say is, don't be surprised if she steals all your dragon bones and runs off with the blacksmith. Those blacksmiths know how to treat a lady right.
The one in Riften is really nice - you can put an Enchanting Table in there, and it's got a nice little garden out front. The Whiterun one is just fine, though; you're only 30 seconds from the Dragonsreach enchanting table anyway.
Onyx - keep an eye out for your wife coming home with coal stains on her blouse... telltale sign.
The easiest one to get is in Whiterun; you can buy this house after (spoiler)you've killed your first dragon.(/spoiler) It'll set you back 5k.
Houses in the other towns, as LordBlades said, require you to do some quests for the Jarl. Most Jarls will want you to do some odd jobs around town before they make you Thane of the town, and offer you residence.
EDIT: Onyx put it better than I ever could.
Me too...It should be noted that you can get the house in Whiterun before the aforementioned spoiler. You need to have completed the quest prior to battling the dragon. Damn, I play the beginning so damn much.
another question. how do you marry people? lol
More importantly, can you divorce the whining bitch when she becomes just too annoying to live with?