Anyone here have hands on with TPM sensors

I have an 09 Nissan Im trying to get ready, at least two bad sensors, batteries prob. dead. One guy told me that no matter where I got the sensors theyd need to be activated and programmed for the vehicle, my buddy at Kaufman yesterday told me that I can go on E-bay, type in OE 09 Altima TPM sensors and put them in, the vehicle would recognize and automatically read them.

He also told me I could get them on E-bay cheap but looking there I see they are really no cheaper than local parts store wants ( 50 a piece )

So whats the truth about these things?

Car is for re-sale so I dont want to spend any more than necessary.