If you end up needing a new TPMS sensor, you can buy a Denso (probably the OE manufacturer) for $38 plus shipping from Rockauto. There's no rush, your tire isn't going to fail because of a bad sensor. For installation and programming, a tire shop can probably do it, but I'd talk to them first to be sure they have the ability to program. My guess is most do. Otherwise, I'll bet any mechanic shop with a tire machine would do it for an hour labor. Those will be the cheapest viable options with a quality part.
However, as suggested here, before you do that spend a dollar or two and get a manual pressure gauge and check it.