I just do sidequests which lead me to ruins and forts and stuff, and I always take the enemy's loot, even if it's just fur armor, or hide armor, etc. It's only worth 50 a piece but it adds up. Usually in every place I visit there's a chest at the end that has some powerful scroll in it, a magical staff, a nice Dwarven shield, some gold and a few soul gems or something. That stuff all gets sold. Then I create potions and sell the ones I don't need. I think I've made a fortune selling potions, because at times I will have gathered enough ingredients to make like 15-20 of a certain type of potion, so I make as many as I can and then sell them. It all adds up.
I dunno, it was pretty easy to build up that much money and still afford Breezehome. Just do more quests and make sure to loot your enemies well. I *wish* I would hover around 1k-3k, it would make buying and selling much more important. Right now it's basically lost it's importance in my game.