I've ordered Salifert test kits from aquatech before. Someone on RC did a comparison and they are one of the lowest priced. However, their shipping is higher than I would have expected for the weight. If you order all of your test kits at once, you might save a few dollars. Don't forget that sales tax applies.
Or if they don't stock it and it is shipped from the manufacturer you pay two shipping costs (happened to me with Hamilton PC bulbs). Be sure to call them and make sure they have your order in stock, and part of it is not trans shipped from somewhere else.
As far as the two part method, I've used it for 2 years and it works great.