First one I bought was on sale @ Performance: Paddington yellow, zip vents and while it is scary-thin, that thing is toasty and soaks up all the sweat. I never feel a drop. +1

I bought a size too big though as I do the first time I buy any new type of function-specific clothing. I recommend getting one that fits. The bigness gets in the way and impedes shoulder+arm freedom of movement. So I use:

I don't know where you live but I have had the best luck at local thrift stores, namely Deseret here in Shoreline. Found a stellar shell in neon turquoise, lined, zippered and adjustable in all the right places...fifteen bucks. Has no tag on it so I cannot ID it for you. I visit them, Goodies and VV's regularly. Found all my underlinings--silk tops, long-johns--plus my REI bike shorts...everything less than ten bucks a piece.

+1 the side/underarm zips.