I've acutally been having problems finding good prices on Salifert online recently and some prices are way higher than my LFS. The last place I got mine from were backordered for 1 month and they said everyone was out even their distributors...I think everyone has stock now though.
I would just buy individually as well. I use only Salifert Ca, KH/Alk and Mg. All the others play a very small role in your tank and should be replenished by regular water changes. I'm sure someone will disagree with me though. The site's sponsor, eReefTank, has the KH/Alk test kits for $12 which is really cheap compared to the other places I've looked. His Ca and Mg kit prices seem good too. If you sign up for his newsletter, he'll give you $5 off your purchase I think.