I don't do much of the shopping, but we get costco frozen burger patties for most of our home burgers. I don't think it costs more than the same weight of 'whole' ground beef, and it's convenient.

Those are thin enough I wouldn't think to stick a thermometer in them... it would be too hard to get it in the center and not out the other side, and it's pretty easy to get a sense of doneness from the outside (or cut into one and see). Steaks, depending on who's eating and doneness preferences, thermometer is nice. Roasts, almost certainly.