If you want a vendor with a decent amount of cash...finish the thieves guild completely. Do the story line, and then do the random quests that will give you the bigger heist jobs then do those. If you do that Tonilla will have 4k gold.
As far as making money...best way I found was to level Enchanting. This isn't my own ***, though, alot of people do it. Enchant iron daggers with banish for a nice little profit. I started off with 8k. Bought a weapon with banish on it for 8k so I could disenchant it. By the time enchanting was 100, I was over 100k in the green. So, taking out what I spent I probably made well over 150-200k doing that.
Now, for what I came here to say, lol: Just made my second character, after 120 hours on the first one. My first one was an imperial who dual wielded swords. She was also an alchemist/enchanter/blacksmith so she was pretty much one shotting everything, thought it was time to get back to my roots.
New guy is Khajiit dual-wielding mage. Magic is pretty cool, didn't use it alot on my first character.