As an electronics technician for many years, I used heat guns all the time for shrink tubing, but they were all well over $100...I would think that is a lot of money to spend for casual use. The suggestion of butane lighters is a good one - just be sure to hold the flame a couple of inches below the tubing and take it slow. Another cool little tool is the butane-powered "blowtorches" they make nowadays for caramelizing creme brulee. You can find some of them for under $10. Matchs work, too, and they're cheapest of all.