discount tire is going to be WICKED expensive. I have several hookups and they couldn't do much.
Treaded tires ride like crap and don't last long. Unless you're making a mud truck, I would spend a little extra and get new tires.
I've had GREAT luck with 'blem' tires off ebay. I just got a 35" mickey thompson mud terrain for like 110 shipped brand new. They have to pass all safety tests, but usually have a nick in white wall or something stupid. I've bought/sold several sets for several vehicles. The last set of 4, 315/75/16 tires I got were 550ish to my door.