Makes sense, never really tried out if hair dryers work on not. I agree on the cheap ones, My corded one has lasted a few years without problems. On the topic of tools I also recommend you get a rotary tool, as they make sanding a breeze. It’ll cost about the same as a heat gun, but it was also worth it.
Honestly I’ve found trying to build armor without the proper tools (funny how that works) is very difficult and usually leads to underwhelming results. As costly as it sounds it’s absolutely worth it in the long run!