Any Minolta Srt or Pentax K1000 would give you plenty of opportunities of future lens purchases. I suggest you look for a camera in good working condition, but with signs and scratches, something that the collectors wouldn't even look at.
You'll find a ton of cameras like this:
this costs €50,00 from a shop which tends to be not cheap (he checks all cameras, though, and gives 6 months warranty).
You might find some for $20 or $30, maybe you should add a cleaning, adjusting and lubricating for some $40 or so. Those cameras are entirely mechanical, very robust and were built and sold in great numbers, so you can find them very cheap, which doesn't mean they are not good, they are very good. They will last forever. Beware of the battery problem with Minolta Srt. There are easy solutions. External metering always better IMO any time you have time.
If you insist on aperture priority, anything of the eighties is fine. I would avoid esoteric lens mount. Stick to Canon FD, Minolta SR, Pentax K, Nikon, Olympus if you want to find cheap and very good lenses for a long time. Things like Rolleiflex and Contax (and Leica) will allow potential purchase of very particular lenses. In the normal range (let' say 28, 35, 50, 90, 135, 200) Minolta, Pentax, Olympus and Canon gave very good quality for money. Minolta in particular, and Pentax. Olympus lenses are smaller than usual and if you value compactness, go for Olympus OM-1 or OM-2 without hesitation, or for a smaller Pentax (ME, ME Super, MX). Pentax cameras can be very small, but the lenses are "normal". Olympus made small cameras AND small lenses.
Canon AE-1 has shutter priority not aperture priority. A Canon A-1 has both shutter priority, aperiture priority, and program. They sold tons of them, you should find one cheap, beware of the "squeak" problem. Konica cameras were the only alternatives if you wanted shutter priority, besides the "multi" cameras (with both priorities). Konica lenses were also very good but probably less easy to find.
Olympus OM-10 in its basic form doesn't have manual settings. I would avoid cameras without manual settings. There was an accessory to use it as a manual camera.
Olympus OM-1 (manual) or OM-2 (manual + aperture priority) would be better.
Program? Minolta X-700, and Canon AE-1 Program (not to be confused with Canon AE-1), if you really want to use that stuff. Or a Canon A-1, as said.
A Minolta X-700 is a wonderful camera, and it is auto (aperture priority) and manual (in manual not fully coupled, but the X-500 is), and Program (X-500 lacks program). Uses two normal LR44 (or SR44) batteries. The specification are nothing impressive if you look superficially. But it has a particularly good viewfinder, much above its class, possibly much above any class.
I suggest reading this:
After reading this, come here and read that a Minolta X-700 has 95% coverage, 0.9X enlargement. You do the comparison. Besides, it has the "acute matte" focusing screen, a Minolta patent which makes the difference, the screen is brighter than normal and also easier to focus than normal. Very good stuff.
Some old X-700 develop a problem with an electronic component, which is easy to replace. Mine (1989) didn't so far (touch wood).
PS If it appears I am partial to Minolta, it's just because I also use Minolta.