It's been a while since I've seen a Pet, although I see 64s occasionally. I have two Trash 80 model Ones in my garage. Both have the lowercase enhancement (done by me). I see Timex machines several times a year.
So what are they worth?
The big money is the Imsai and Altair computers. The Timex and TRS-80 machines seem to sell at wildly different prices depending on who wants em I guess. Crap shoot there. Check E-Bay. Pretty good indication. Old Byte Mags (pre 1980) go for a good price as well. ASR-33 Teletypes have become collectible also.