You are correct in your approach. A year back I was faced w/ replacing the set of sensors in both my street and track tires at same time
Believe me I searched for alternatives!
Anyhow, there are numerous aftermkt 'generic' TPMS suppliers which work great (typically w/ a longer battery life too as OEM are usually 4 years) and can be had for ~ $200 for a s/4. Just make sure you provide correct model info and RF if different options for MY.
When replacing just sensor/valve, most shops will 'key' tire to wheel. Then all they need to do is deflate, break bead, remove old / install new and re-inflate. No need to re-balance. Yes, harder to do w/ low profile tires and narrow wheels but these guys do it everyday and they were able to on my 19" wheels (both sets).
Once installed, it will take a few minutes for car to learn new sensors but they typically do so w/in 15minutes of driving and you're good to go after that.
In the 9x7.1 series it's a major PITA that once one sensor goes out the entire system reports failure and will not show pressures for any corner. Oh well, good problems we have as they say...
FWIW, the PIWIS system can query each sensor for "months of life remaining" but unless you know why one may have been replaced at a different time than another, it's best to treat like headlight bulbs and replace all at same time.
Good luck
PS - and don't cheap out buying used which people constantly trying to swindle others w/ on forums/ebay/etc. Particularly when you can get new for ~ $50 each (or less).