IDEA: Merchants gold is dependent on their mercantile skill (is mercantile in the game? If not then higher/lower prices at shops). If the shop has a lot of gold, you will need a high merch skill to get the most out of it. Either that or a system like fallout (not the first game to do that) where they have a static amount. Or, have them like in Oblivion but say 20 000 gold which will get totally depleted by a super item but will take time to 'recharge' as he sells other thing, either to you or others.
Right now in Oblivion I have ~100k gold and I haven't really been looking for it. I was strapped a while back but I set out to make some money, mostly through thieves guild.
I DO NOT like the idea of grinding for money though. In a world like this it should be easy to get if you do quests or dungeon crawl or steal.