I don't think you can go too wrong with a Robbins top, I just fit one on my 3A and am very happy with it. Of course there are more expensive options out there if you want to go mohair or something, but for vinyl I think Robbins is what I'd pick.
Internet is your friend in finding best prices, TRF, Moss I think carry Robbins - I bought mine from topsonline.com and think I save a few bucks at least when I bought it earlier this year.