After finally running my new car for a couple laps I think I’m ready for some racing! My question is tho, what’s the difference between 3 wire and 2 wire transponders. Which one should I get and does anyone have one for sale? Is it something I can get used?

Yes, feel free to get a used one if the price is good. The old ones are just as good, I have two of them and don't plan on getting a new (small) one until they stop working. Just check the wires on the exit of the cases, it's a weak spot (on both new and old ones). Also check the compatibility and the system your local track uses. The 2 wire one is a safer option and is compatible with all

2 wire would be safer . i have one a 2 wire for $75..

2 wire, RC4 hybrid is backward compatible with the older systems.
3 wire works only with the latest RC4-system.