if you play on PC, the easy (but temporary) fix is open console, click on merchant, type:
additem f 4000
Yeah, seems a bit cheap, but what is the alternative? Going through hoops because gamesas yet again didn't care to provide any link between item worth and the amount of septims actually in the game? Use exploits? At the end of the day, it's simply faster to add the gold directly and pretend to have waited for half a year to sell off all your loot, about 1000 septims at a time, than it is to actually be bored senseless waiting that long.
And yes, you can barter with merchants but unless you go all in with Speech perks (and that's not really a sound investment, perk-wise), you're going to end up buying stuff at twice it's actual value and then be able to sell it on for maybe half it's value. That is a rather huge loss, isn't it?
This is what I do, but instead of calling it "cheating" I call it "immersion."

I mean, I don't think it's reasonable that an entire city can't support a single adventurer selling things he found in one dungeon at less than half their actual value. And apparently, the traders the adventurer barters with aren't very competent, considering they only ever seem to break even when reselling the items.

Hopefully in the future someone will release a mod that reworks the entire money system, and maybe even implements more things to do with money, (besides houses/training.)
I think money has the potential to be an interesting motive/mechanic for the game. After all, it's basically why the Thieves Guild and The Companions exist. From early interviews, it sounds like Bethesda was going to make trading an interesting mechanic- messing with the economy of Skyrim, etc, but then scrapped it entirely for reasons they've never made clear, (something they seem to do a lot.)