The running cost is where people get caught, and it is worth doing the arithmetic before rather than after.
Add up: the device, the subscription for twelve months, at least one replacement collar, and — if it is cellular — the fact that a subscription lapsing usually means the device stops reporting entirely rather than degrading to something lesser. Check that last one specifically before buying, because a tracker that becomes a paperweight the month you forget to renew is a different proposition from one that keeps working locally.
The thing that actually decides whether you still use it in month three is charging. A cellular tracker with live updates wants charging every few days. That means catching the cat, removing the collar, remembering to put it back on. Miss it twice and the device is flat in a drawer on the one night she does not come home, which is precisely when you needed it.
So be honest about the update interval you will really live with. Most of these let you slow the reporting rate down, and the difference between updating constantly and updating every few minutes is enormous for battery and almost irrelevant for finding a cat who has been missing since yesterday. Turn it down on day one. The default is set to demo well, not to run for a year.
The device that is charged is better than the accurate one that is flat.