I purchased a used Brother PQ1500, mechanical, straight-stitch only, knee lift, auto threader, 1500 spm, thread cutter for $400. I've had it for 13 years, keep it clean and oiled, and have never needed to take it in for repair or maintenance.
About 17 years ago, my husband had purchased a smaller machine for me, a Brother SE270D. It was my daily driver before I bought the 1500. I keep it because it does buttonholes and other decorative stitches. It's computerized, and the LED light finally started dimming. I couldn't figure out how to replace it, so I took it to the repair tech who told me that machine is considered disposable and the light is not replaceable. The manufacturer assumes an owner will replace it after 5 years or so of use. Well, I thought that was ridiculous, the machine itself still works perfectly, so I bought an IKEA Jansjo lamp to light the work area when I use that machine.
Not sure if I answered your question or not; I got lost somewhere in your post as to exactly what the question was.