What I'm currently using is a $12 human heating pad from Amazon, set to low. The first day of use requires pretty frequent monitoring and some adjustment (my roaches are at the perfect temp with half of their tub sitting directly on the mat, but I had to get crafty with a hot glue gun and some cardboard to make little feet for my superworm bins so that they could sit slightly above it and not overheat), but after that it's pretty simple! I use an infrared temp gun to check my temps every other day when I put in fresh fruit/veggies for moisture, just to make sure nothing goes wrong, but so far it's been a very convenient and affordable solution for me. Much more so than reptile-specific undertank heaters that would probably get too hot, and cost a lot more for the same size. One of these mats heats the warm size of my roach tub and the warm sides of three separate bins for supers!
The dome fixture and bulb you mentioned will probably work in a pinch, with some monitoring and adjustment to make sure you're getting the right temperature range, but personally I'd move to something that doesn't put off light when you can. Roaches in particular really don't like to be exposed; they like the dark!