You can make a DIY LPM for that much, but it's a catch 22 since you would need lasers of a known power, to calibrate with.
If you really need a calibrated LPM there are two options... Laserbee and Bluefan... where budget LPMs are concerned.
If this is a one time thing, just see who's close to you with an LPM and can test it out.
I would do it, but I sent one of my LPMs out today, and sending out the other one tomorrow to a friend, so we can compare calibration.