I knew you’d succumb to the siren call of REW before long! You only need the SPL meter once, to calibrate the mic level. Maybe you could borrow one? Although HST, I do find mine useful to own.
Download Jerry's REW Setup Guide if you haven’t already - it is a WIP but it already contains loads of useful info. It's linked in his sig.
All my friends and acquaintances are technically illiterate. I'll just have to stop by the local RS and pick one up.