I am planning to get a used SPL meter from eBay, the older RS model, the 33-2050 I believe. I'm in Canada, and I haven't checked, but I'm sure the new analog model, the 33-4050 is probably $60 CDN or more if the canadian radioshacks even carry it!
One question I have is: is it important/better to mount the SPL meter on a tripod? I'm asking this because I guess while you're holding it in your hands it moves around and probably causes "noise" when being held and shook, etc.
It isn't critical. The recommended settings for adjusting your speakers is 'C' weighted and slow response.
What *is* important is that you not stand directly in front of or behind the meter while taking the readings. Your body can both shadow and reflect the sound you're trying to measure.
I always sit to one side of the sweet spot and hold the meter at arm's length, head height, and pointing up at the ceiling. Meter in one hand, remote in the other, and make the adjustments.