repeating what everyne is saying....
get into caves/dungeons and take armor/weapons from baddies.
Also, join the Arena and beat it so that you can go back once a week and fight monsters.
If you chose to fight all 3 creatures at once, youll make 3 to 5,000 gold in under half a minute.
right now Im at around 315,000, and Ive already spent 60,000 on the skingrad house, 5000 on the haunted manor, and 5000 on the waterfront shack.
Like Krimson said, not much to buy in this game, and I only bought those houses to finish Quests.
I have never bought a single piece of armor or weapon. The only $$ I spend is on enchanting items at the enchanting altar, and that hardly costs anything.
Up until I Feathered everything, I was making 5 or 6 trips a cave to be able to carry it all to the shops and sell it, pain in the ass. Now I can carry 1072 lbs and do it all in one trip usually and make 10 to 15,000 gold a cave if its got the right enemies(vamps/bandits).
The Oblivion Gates are full of Daedric stuff obviously, I had to pick and chose what to take out, its all very heavy usually. I walked out of my first gate with 1070/1072 carrying capacity