You can try a radioshack SPL mic (~$30) if it dosent show your SPL (only goes up to 130dbs I think) then you need to upgrade you mic, and if it dosent read up to 130dbs (ie 120) you need to upgrade your system //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif
Also some local shops have mic's they charge to use for a few minutes...