I can afford whatever the price they're selling them for no problem. Armor: Best for sigil stones, with four peices of any armor, I can get 100 chameleon. However enchanting also has a 'max enchantment' on an item, meaning you can't put every effect you want into one. Yeah, I'm at the point now where I want to start putting perks into the Enchantment tree and I'm gonna need some good gems to increase my enchantment strength for items I apply it to. Enchanted however is an unlimited source, just fill up a soul gem, the effects are choosen based on your spell inventory. If only I could make a mega soul gem of some sort, I'd be even more Gollum for that. I love the effect of the soul trap spell, and I must have every soul I can take. Take it from me, I'm a guy who has something like a hundred pounds of soul gems by now. But if you want soul gems coming out of your ears and a serious amount of gold spent in one spent, it's the College all the way. You will find 2 black soul gemstones during the cheydinhal suggestion quest, nevertheless theywill end up being used from you at the finish of the mission. 0002E504 Black Soul Gem (full) 00043E26 Wylandriahs Soul Gem 00063B27 Azuras Wrath.
Otherwise, it's court mages and pretty much any merchant that sells items out of the 'Misc.' category. Best place with Elder Scrolls V: Skyrim cheats codes, secrets of the world. You'll sometimes even find a black soul gem that's already filled at the grand level. Your best bet otherwise are ruins that are rife with necromancers and conjurers, especially when you get higher in level. Plenty of soul gems of all kinds, and the only two places I know of with merchants selling black soul gems. Falion in Morthal and the College of Mages in Winterhold.