the short answer is, the VAST majority of traders have 1000 gold or less. BUT....
i usually sell most of my unwanted gear to the blacksmith in Whiterun. you can initiate a conversation with the woman outside smithing, and ask what she has for sale. Generally she has around 800-900 gold and a bunch of smithing materials. Buy a bunch of good ingots from her (malachite, dwarven, orc, ebony, etc) which increases her gold count. Then sell her whatever you want.
Next, walk inside the shop and deal with her father. He generally has about 1100-1200 gold. Repeat. These two will only buy armor/weapons/smithing items, so save your misc stuff for.....
Then walk down to Belathor's general goods. He has 700-800 gold. Sell him misc junk that you've collected such as skill books, pelts, unused potions, jewels, etc.
Lastly, go to Dragonsreach and speak to the wizard. You can sell him enchanted jewelry, scrolls, staffs, and soul gems (although i would only recommend selling the enchanted jewelry...the rest of the stuff i use). He usually carries around 600 gold.
All in all, you can probably sell about 4000-5000 worth of stuff off one trip. This is assuming you bought stuff from the vendors too, to increase their gold count. Also, its assuming you dont use the investor perk that allows the vendors to have more gold.