Measuring SPL with a microphone and software

I really want to get consistent monitoring levels but I don't want to go out and spend money on a spl meter if I don't have to. Anyone know if theres a way to measure the spl of monitors with a microphone and some type of software? Is this possible or do I have to bite the bullet and just purchase an spl meter. Also if anybody has any tips on how to calibrate monitors that would be great.

Try borrowing one. My SPL meter is one of those things that sits in my kit bag 363 days a year or so and is low priced enough that I would certainly take the risk to lend it out without need for a deposit. Maybe another engineer or musician you know has one? I would ask around. I would agree you probably won't use it enough (once you get calibrated) to justify the expense, although it is true, as said above, that it's a pretty small expense (for audio gear anyway).

If he borrowed one... he might come across the same question as I did: Which SPL of about 80 to 85 dB should one refer to? Meaning...: * dA(A) (human hearing weighted) or dB(C) (unweighted) ? * slow or fast response (in my case 250ms or 1000ms integration time) ? * peak (max hold) values or more average RMS-like? To my ears 85 dB a-weighted with fast response and peak/max sounds just right.