I found a wand worth alot of gold, where is the "richest" vendor?

In a vanilla game without add ons, Morvayn's Peacemakers in anvil give up to 1200 gold for an item, with official add ons, Nilphas Omellian in the Merchant's inn, IC market place has 2000.

1200 is not the limit without addons. Fjotreid in Bruma has 1300 gold including investment

Those numbers are the base before investment or Mercantile Mastery. At max, you can get 2200 from Varel Morveyn, that's the base 1200, plus 500 if you invest in his store, and another 500 if you maxed out Mercantile. There are a number of other merchants that have 1200 gold per purchase, but the others have a higher skill and are harder to haggle with. Once you hit max yourself, haggling isn't an issue and Rasheeda, Palonirya, and others pay the same, and of course, buy anything.

Fathis Ules, the top fence for the Thieves' Guild has a 1500 base gold, but you have to be a high-ranking TG member to sell anything to him, and if you made the choice he doesn't like about the Honorblade of Chorrol, he won't deal with you at all. Mods official and home-brew add merchants with higher base amounts.

Best to treat all "values" over 1200 as just an indication of the power of the enchantment, rather than a gold amount. If it's an enchantment that doesn't matter to your play style, it's not "worth" anything.