Not sure if you know this or not but you can send them your own sample without ordering the Beer Kit. Go here:
Read the instructions on the bottom of the page. Most people seem to use a small plastic vodka bottle and they will ship it in a USPS flat rate box. The household mineral test is $21 and the Brewers test is $27.25. The Household mineral test includes:
Total Hardness (Lime)
Est. Total Dissolved Solids
The Brewers test includes all of that above plus Iron and Phosphorus.