I was in my local Walmart to buy a cheap trailer ball and noticed some sound meters over at the car audio. I know these aren't great but they will work well to test modifications to your exhaust to see if it is quieter and are digital with a Min/Max memory function. Heck, last time I wanted to buy one the cheapest I could find was $150. RadioShack used to carry a $75 analog model and a $100 digital but since CircuitCity took over they stopped selling them in an inventory cut back move.
