I don't have a horse in this race, but Spa Depot has worked well for me. I don't order often, but usually order about $150 worth of stuff at a time.
SpaClear 2# $ 9.95 ($4.98/#)
SpaClear 4# $19.95 ($4.99/#)
SpaClear 6# $26.95 ($4.50/#)
303 Protectant by the gallon for $49.95.
Free shipping, but $2.95 handling fee per order.
I buy Nature2 on ebay at 4 for $58 plus $7 shipping & handling or $16.50 each.
BTW, it all still seems overpriced to me.