TPMS Sensor replacement

2016 prius

I needed 2 new tires so went into the tire shop and got them done. This was 2 days ago.

So today on my car got the flat tire light to go on. I went back to the tire shop and he said 2/4 sensors look to be going bad.

I told him the sensor was not on before the tires were changed. He said they were probably going bad, (i bought the car 5 years ago ) and replacing the tires made them lose the signal or something like that. He said they can replace the sensors at the tire shop which saves like $200 from the dealer.

So my question is am i getting ripped off here or is this guy legit? Like I said, before the new tires, the light was not on. Or is he correct that the sensors were 5/6 years old and going bad anyway and needed to be replaced.

Part 2- anyone bought these sensors over amazon? I see 4 non-OEM of them are much cheaper than the tire shop but from the reviews half of them work.