I bought a used May 2017 MX 75D this summer from Tesla
A few suggestions:
1) this is a great site to search inventory and apply the filters you want:
TeslaCPO.io - Search Tesla's Vehicle Inventory
2) I was moving from a 2017 MS with FSD and had a few specific things I wanted: non-black interior, 6 seater, < 30k miles - that's it. I ended up with this one:
TeslaCPO.io - Search Tesla's Vehicle Inventory
I spent $500 for a tow hitch and $2500 for the MCU2 upgrade - both happened at delivery. Inspection was good - just like the pictures and no major issues or area of concern. It already had FSD, so the MCU upgrade not only helped with a few FSD features, but made the car feel like new (Especially coming from 3 years in a MS with MCU1 - the new MCU is lightening fast). My range is 240ish miles, essentially the same as my MS75, so the MX100, to me, wasn't worth the almost $10k premium a few months ago.
The price was fair and $1,000 transportation to me was fine. Out the door, it was $63,100 with transportation, tow hitch (which is usually over $1200 installed, but they took off the bumper and added the tow package for only $500), and new MCU. I don't miss free supercharging, as the few times I've supercharged this summer it cost me less then $7, so I wouldn't spend enough to really consider it free supercharging a perk.
The prices drop almost daily on used inventory, like a reverse auction - wait until you find the price you'd be pissed if someone else bought it and pull the trigger. If you find you can't find a car with everything you want for substantially less than a new one, then I'd probably go new or wait until after battery day on 9/22 in case they tease a new model.
Good luck!