Steal.
Everything.
It's quite fun. Though everybody is in their underwear now. and I mean EVERYBODY that I could loot.
Yeah .... Hey, I need to pass the time somehow!
Steal.
Everything.
I hear that investing with the merchant in Riverwood really ups his available gold. To the tune of 11k. Too bad you can't buy a house there.
Yet.
So the first time you come across one, disenchant it, instead of selling it. From then on when you come on an enchant table, you can make as many "with banish" weapons as you have unenchanted weapons and filled soulgems. And as far as merchants not having enough money, until someone comes up with a lore driven way to enrich Skyrim's merchants, you might try the Rich Merchants mod. It can relieve your stress.
enchanting(Talos knows how much this'd get you)
Two iron daggers enchanted with petty banish cost more than what any merchant can pay for.
The problem with banish is that you only rarely come across it, hit or miss.