As a hockey player, I understand that under armor is just spandex, but a full bodysuit spandex. A scuba suit will work just as well, probably better, because sometimes under armor has those stripes on the side. Under armor suits will have a neck brace, but it is not very good. Unfortunately, this sounds weird but the under armor that is only available to me is the one with the jockstrap built in, so it's not very good for MC's armor, unless you're building around that.
Where I live, under armor suits get really expensive, upwards of $100 CAD (Which is just about $100 USD for those of you who are in the US and not keeping up with the exchange).
It all depends on what you want. If you look in local sports stores, there could be a cheap suit on sale, or you could buy the shirt and pants separate.
I'm just using a black long-sleeved-T-shirt and black pants. Because the mop on top of my head seems to be forever growing, I don't think I'll need anything to cover my neck.
Also, if you need something to cover your neck, go to the sports store and pick up a hockey neck guard for about $10 and wear it inside out. Also, tuck it underneath your shirt if you don't want a tag sticking out.