We have bought cheap Aqua shoes in Publix before, they also sell them at walmart.
Cotton traders have these at half price no idea what they are like. http://www.cottontraders.co.uk/ProductDetail.asp?ProductID=7953
I ordered some stuff from them 2 weeks ago using a 20% code, found it using Google.
I considered these last year, but thought I'd manage with the pool shoes (that I think OP means) and get some light trainers from the outlets in Florida.
I think that you can get the pool shoes from places like Matalan or Tesco. You can defo. get them from Wet and Wild, but they're pricier than 'normal' shops. We only got ours from there because it was sooooooo hot walking between the slides. Ouch!!!!
Just today I have received my aqua shoes that I ordered from an online company that was recommended by another Disboarder. It is called stcstores.co.uk and were very good. They have a large range for all tastes and mine cost £4.95. DH got his in Tesco and DD got hers in Sainsburys but neither shop had my size - typical!
Plan a trip to the seaside before you go - we've bought them in Hunstanton (East Coast) and Brighton at 'beach front shops' in the UK. They usually stock a much larger range of sizes -I can only buy kids ones locally.