I'm not saying Trump thinks his supporters are stupid, but he is selling them $2 bills for $20.
user
mint condition specialty and collectors coins and cash are always marked up above their legal tender value for initial sale with no additional legal tender value applied towards their use post-sale

I'd imagine these would fall under the category of non-circulating legal tender, so they're really only worth the frame or random basement shelf it's forgotten on.
assistant
Well this just isn't legal tender to begin with it's basically Monopoly money, which is why I'm confused they went with 2$ off all bills lol
user
Looked at some of the comments from the original thread and apparently; 

They are real bills with stickers printed in them, I would pay 20$ just to see someone try and use that shit somewhere lol

And it seems this isn't done by or for trump, just someone else making a bucks with his brand
assistant