bad tpms monitor

How does one change a bad TPMS censor on a 2006 Acura mdx?? Is it hard to do?? My TPMS light stays on and a guy at walmart said my rear left censor was bad. Walmart doesnt carry that censor . I'm sure an Acura Dealership will rip me off big time. The censors are $40 on ebay.
THANKS

You will need to dismount the tire. There should be a nut holding the TPMS assembly and valve to the wheel. Just undo the nut and the TPMS should slide out, towards the inside of the rim. I recommend you take it to a dealer or auto shop to do it....

what year, you may have it under warranty if it's confirmed...

also, www.acuramdx.org is a good site as well for this