Questions about the upcoming Nats

I'm planning on go to the Nats in Columbus next Saturday and I'm wondering do the venders on the manufacturer midway actually have inventory to sell or are they just promoting and taking orders ? Any show discounts ? Last question I'm wanting to drive my Duster but I'm curious about parking , I don't want to be parked in some tight parking area ? Only going for the day so paying an entry fee doesn't make much sense .