Quoted from vid1900:
Pretty normal for something you use to lose value once you use it.
Other than a few titles like TronLE, there are not many pins that go up in value once you opened them.
If a used MM is $5,500, you will not be able to restore it to the level of the MMr for $2,500, that's for sure.
New decals for cab $300
New clear ramps $400
Clear coat the playfield $500
or Replace playfield $900
Color DMD $400
Flipper rebuild $25
Moat $50 (always cracked)
New plastics $150
New dragon wings $20 (always broken and glued)
A million other worn or broken parts as you restore $1000
Stereo sound N/A
80 hours of your time @ even $25/hr is $2000
Don't kid yourself how much work it would be to take a used MM and turn it into a game anywhere near as nice as a MMr....
I had close to $4k (above the core purchase price) in a full MM DIY restoration with all of the above plus a number of mods, and that was excluding my time which was over 240hours.