I paid 200 CAN$ for a set of cheap 26" wheels. I had horizontal dropouts. You'll need a new chain and perhaps a chainring. If you change your crank, you may have an issue with your bottom bracket - you may need a longer one). You may or may not need to do that to have a nice chainline.

You're looking at about 250$ for cheap parts if you do it yourself.

It's worth it though, converted my old rockhopper last week. It's a blast!