WOW! I did some looking to try to find the brand I had used as it worked well for several different RV as we traded around way too often. The price has jumped way too high for logic as we were in the under $200Range a few years back. Looks like they have found they have a sought after product so the profits went way high!
I suspect there was no real TPMS on the RV but it needs checked.
Do you see any sing of anything really different on the wheels at the valves? TPMS have to have electronics to send the signal to the front and they will look different enough for an untrained person to spot them.
If they are stock OEM the valve stems look different and when first turning on the key there should be some form of light come on to indicate the bulb or alarm is working.
Like you get for the brakes and all those other things that light up when we first turn the key?
But if it was aftermarket, there should be some form of monitor added somewhere around the dash. I might guess odds are about 25% of having a real TPMS??
For what they look like, they come in lots of brands and lots of shapes but this is one source for them.
https://www.etrailer.com/s.aspx?qry=tpms
But I didn't know the price had jumped so high!!