I use an O'Donnell temp "gun" that I used for my nitro stuff, $40. The big thing about temping BL motors is that thier normal operating temp. is any where from 165deg (Novak) to 200deg. (Castle). The major reason you need to temp these motors and not just use the "touch" test is that a motor that can run all day long at 165 may blow up or at least shorten it's life by running it at 185deg. At those temps you can't tell the difference by touching it.
I don't really think you need to get a $100 IR temp gun but at least buy a quality piece. You spent all that money on BL, spend a little more and keep it alive! Some temp the can and others temp the endbell, I keep both under the recomended temp.