I don't see the point in a temp gun if you have a thermometer with a remote probe.
I've mostly used mine for checking the temperature on the ground when doing the annual herp hunt, and pointing into my kids' ears to check for fevers. I've virtually never used it in my reptile bins, because once the bin is opened, the temperature immediately changes, so it's pointless. Don't get me wrong, it is occasionally useful, but not what I would consider an essential piece of equipment.

A quality thermostat, which runs over $60, is essential, but not a $10 temp gun.

In order of most important equipment:
1) Thermostat
2) Heat source (Heat mat, heat cord, heat tape--not a heat lamp).
3) Thermometer with remote probe

After that comes hygrometer, cage, water bowl, hides, etc. You can make a good cage out of an $8 plastic bin, a soldering iron, and some strong clips, but there is no substitute for a good thermostat.