I totaled my 2019 Prius in January of this year. Fortunately, I came out without a scratch! I have two key fobs that are sitting in my drawer. One is brand new as I got it as a replacement a week before I totaled the car. Can the fobs be reprogrammed and used by someone else? Not sure what to do with them. Also have the original owner’s manual if anyone needs it. Will greatly miss my Prius, but decided to go with a RAV4 hybrid this time around.
A brand new FOB that hasn't been programmed to a specific car yet is fairly easy to set up. To do the same with FOB already connected to a vehicle is possible via an electronic locksmith or someone with access to the security section of Toyota techstream software to perform a wipe and reseed of the system. Also there's a business in Europe that does some complex math with your VIN# to get the security code to do a wipe and reseed in Techstream. But in general you won't be saving any money and will experience considerable hassle setting up those FOBs on a different vehicle.
I got a used 2019 Prime, which only came with one fob. I got an eBay "deal" on a second one that they claim was "unlocked" (whatever that means). The local dealer was able to cut the physical key and program it for my car without any problems. For a little while, the car had a message about the new key, but that went away after a little bit. I don't know what they did to unlock the fob, or how it's locked. But it is theoretically possible.