You say you're a budget racer, I can understand that, been there done that. Still, I found the air density gauge to be very useful, if not essential. Air density and getting the right jet for the ambient conditions go hand-in-hand. People will tell you that these small engines don't respond to air density, trust me, they don't know what they're talking about. In my 50+ years in and around karting, I made a lot of mistakes, I did a few things right, and buying an air density gauge was one of the things I did right. Longacre, on the net, they sell the gauge, has some articles you might find interesting.