Is it cheaper to replace the thermostat and pump at same time vs. separately?

This is a tough question, and a lot depends on the shop doing the repair(s). Also, on virtually every vehicle, this is 2 separate jobs. If the shop simply charges by-the-hour, the coolant is already drained to do one part of the job (say the water pump), so it will save time changing the thermostat. If the shop is a "flat-rate" shop, they will charge you the time the labor guide shows for EACH part of the job. The catch is, the shop that charges by-the-hour may estimate more time than the "Flat-rate" shop, so you could pay more in the long run. The best bet is to get estimates from several shops. It's very confusing, but I hope this helps you understand a bit better!

t-stat is so cheap you should have it done at the same time if you have any doubts about it at all, the whole deal should run about $100 with parts.

in all reallity you should replace both at the same time ...