I picked up some Kenyon Polartech Powerstretch undergarments from Sierra Trading Post last year. With the Frequent 35%-40% off & Free Shipping coupons from their dealflyer they were around $35 total for the set. I've used it as a baselayer under an MK2 in 40-45deg water comfortably or mid summer alone in 65-70deg water but I'm not very prone to cold. They are cut long and overlap each other really well like the 4th elements.
Right now they only have the bottoms:
Kenyon Polartech Powerstretch
Right now they only have the bottoms:
Kenyon Polartech Powerstretch