Try the discount aisle/section of sporting goods stores, camping stores and ski shops. Look for something sweat wicking for your underlayer as you will sweat and maybe a fleece (preferably a stretch-fleece) as your insulating layer. You can always cut the neck off and make it a crew neck; fleece will not unravel. That way, both layers are washable.

What BCD said about market share is true. that's why no major sporting names have targetted the coldwater dive market yet.