If you’re going to dedicate a radio to APRS there are some things to keep in mind.
1) It doesn’t have to be powerful. All you need to do is reach out to the closest digi. In fact, having such a strong signal that hits many (there is nothing wrong with being able to hit a ‘backup’ digi) digis is only going to interfere with :
a) another station trying to hit the digi at that time.
b) other stations hearing the digi. (remember, we’re all on 144.390)
and typically this kind of thing will kick off a whole lot of re-transmits which will no doubt walk on each other yet again and cause a big vicious cycle.
2) You’d like it to work unattended. What if there is a power glitch ? Do you know for sure no matter what the radio will come up at 144.390 simplex ?
3) Small(ish) would be nice.
That said, consider a ham-fest treasure like an old crystal controlled rig, or something with thumbwheel entry like an IC-2AT or a Kenwood 7600. These radios don’t have memories than can get scrambled. They just fire up and work. Links to photos below.
Radios don’t last forever and from experience I know you can spend more on replacement power transistors for a boat-anchor ‘7600 than what makes sense. Don’t pay too much. You’ll need some computer gear next.