Auber Ins was very fast with getting back to me. I had just asked him the same question as the OP.
If in AUTO and you switch RTD inputs, the PID will be totally confused. If you are in manual mode switching is no problem (as long as you are not concerned about the calibration of each RTD) NOTE: if you switch make sure you have a good switch
"1) To do that, you need a very good DPDT switch that has very low contact resistance. 1 ohm of contact resistance will give 3 C or 5 F of error."
So it looks like a cheap PID is the best way to go if you have many RTD's and switch between them (just make note of differences in calibration between them - The offset is fairly consent I gather so it will just be +/- a constant that I will post next to the switch). My control panel is full, So I think I will order the cheapest Auber PID (SYL-1512A), some panel mount disconnects for the sensor wire, a switch or two, and get a box from the hardware store to house it. Not worried about using it to run anything so no SSR or heatsink required.
BOBBY M - just looked up DWYER - looks like Series 40T/40M Digital Temperature Switch would be the model, but it is $50ish compared to $30ish from Auber.