There has been some concern about the price creep in doing a properly eq'd multiple sub setup. For a one time deal the hesitation in spending $200-300 in measurement hardware is understandable.
In a nutshell what any one that wants to build and setup a high quality, cost effective sub setup can do is get an SPL meter for $60, or even try an SPL application for the iPhone or Android.
Armed with that they can do the
sub crawl approach. You are going to need a friend and some time how ever to complete the sweep of the typical 20-80 or 20-100hz range.
Figure out your reasonable placement options for the subs and start crawling those areas with the sub in your typical listening position. You will want a piece of graph paper for each of your potential locations so you can construct a SPL to Frequency plot. You will need someone that can use a computer as a tone generator and start playing back tones at 2 or 3Hz intervals and record the SPL levels at locations and construct your graph.
I am personally thinking about starting a rental service of my measurement rig.