As you consider the advice in the comments above, please also consider the fact that virtually all high school and community college photography courses in the U.S. require that the student use a camera capable of fully manual operation. The most commonly suggested model is the Pentax K1000. Its features are:
- Robust build
- Fully manual focus
- Decent viewfinder
- Internal light meter coupled to both shutter and lens aperture
- Mechanical shutter
- Manual film transport
- Compatible with all K-mount lenses with an aperture ring and almost all M42 screw mount lenses
The MX is all of the above with several other nice features thrown into the mix...such as:
- Very compact
- Pro build
- Full-information viewfinder
- Self-timer
Bottom line is that it is a very capable fully manual, metal, K-mount body that was originally marketed to professional photographers. Unfortunately, they are a little expensive now days, but then again, so are K1000s. My general advice is to forget both and get a KM or KX.
BTW...in regards to the MX being an "old" camera. Yes, the last MX was made in about 1985, but that hardly makes it an antique. Half my cameras were made before 1970 and those take excellent photos and are merely considered "vintage". What you get with cameras like the MX is a repairable body and build quality that is generally lacking in most of the AF cameras that came later. Spend five minutes with an MX and then pick up a SF1 or any other of the plastic cams and you will see what I mean.
Steve