Yeah im having that same problem with the paint brushes. I got four today for $1 each. You can also use acetone on the brush while the resin is still wet to rinse it out. You might get like 2 or 3 uses out of your brush that way. I advise taking that visor out now, before it gets too hard. Resining the helmet was the easy part, put the fiberglass on is hard. I'm on my second coat now.
Yeah, i thought i wasnt going to get any resin on it but it ended up getting on there anyway. But putting on the fiberglass cloth isnt to hard, you just have to be very patient (this is where im losing my brushes.) When you cut the fiberglass try to make the cuts are as clean as possible. Some of it will come loose and get stuck on the brush.