for the price-conscious (AKA just about everyone), you might want to consider the $21.00 Household Mineral Test. the only difference between it and the Brewers Test is that you lose iron and phosphorus. personally i have never looked at iron nor phosphorus, not sure what i'd do with that information anyways... i'll be saving myself $6.25 by going with the cheaper option.
fyi, if you have too much iron in your water, you'll know - beer will taste like blood.
phosphorus shouldn't be a problem unless you live in a very agricultural area - fertilizer runoff could jack up your P levels, but this will vary throughout the year (rainfall, growth phase, crop type/rotation, etc.). however, if you or someone you know have kidney disease and are on dialysis, phosphorus levels matter and you should get the test. then again, if you have kidney disease, i'm not sure drinking beer is a great idea anyways...