Also, you can get your enchanting and smithing skills up too.
Things you'll need:
- Iron Daggers (make them, all you need are iron ingots and leather strips.)
- Soul Gems (all kinds, they just need to be filled)
- Enchantments (i have found that the best enchantment to get the most cash are the paralyse and drain health, paralyse make slightly more)
Let's get started, pretty straight forward. All you need to do is make as many Iron Daggers as you can then go enchant them with paralyse or drain health.
Filling Soul Gems is easy, just get out there with an enchanted bow hunting everything with fur on it and you'll have tons of soul gems.
Iron Daggers by themselves are worth about 10 Septims each but enchanted they are worth anywhere from 120-600 Septims each. Unloading the daggers you'll only be able to sell a couple cause let's face it, the shops only have about 1000 Septims so make sure to buy all the leather, leather strips, iron ingots and soul gems as you can too. Don't forget the Thieves Guild fences when selling your goods.
Now get out there, make some cash and buy that house in Solitude legitimately.