Dig deep and spring for a metal Canon "F" series camera, FTb or first or second gen. "F1", all large and heavy, so you know you've got a real, manual SLR in your hand.
They have mirror lockup, depth of field preview, self timers, solid machining, sound meters, if working, even with a SR44 batterie in a diode voltage case or by addition of a Scotts diode, and an "O" ring spacer and they will give you a true, manual, learning experience.
The size and weight of the camera is greater than the Pentax k1000 and many of these cameras that were made in the years after it became available but that serves to keep you mindful of what you are doing, which is getting a good picture.
I suggest all your shots include a preview of the depth of field, which will allow you to select the setting you need and condition your mind and vision on what will be included or no, in the photo you're about to take.
The Canon FL/FD lens system on this camera will also allow you to use other maker's lenses, such as the M42 Pentax/M42 Universal mounts and there are many, many thousands of these out there, many excellent pieces of glass, for pennies compared with more sought after Canon FD lenses (by video and digital makers) whom have driven up prices on the fine optics.
Learning on the FTbn QL will be fun and chances are good no one will knock you down for your old Canon camera, it's a dinosaur in mint folk minds and eyes now and you can bump back with a metal brick, if need be.
You should be able to find a Canon FTbn for about $50US, if you take your time and look around.
Remember also the 50mm f1.8 kit lens that came with these cameras also is a very well regarded lens by many, so you're no starting off 'deprived' of good glass, starting off.
Just remember to use that depth of field for every shot and pay attention to the basics.