Is a Prusa Mini+ for $100 a good deal?

Yeah that's a good deal if the small print bed is what you are needing. Just make sure you buy from a reputable seller.

Unfortunately the guy never responded on marketplace

if the printvolume suits your needs, i guess it's a good deal. the prusa community is great and the printer is well supported

What about the print quality, I don’t mind speed
- It's OK...nothing stellar or impressive, but acceptable and absolutely good enough for most light users, the one-sided Z-axis is not ideal.
  
  ~~But yeah, the speed is completely shit compared to other modern bedslingers.~~ edit: seems they managed to catch up to the cheaper competitors WRT speed, so they're on par with printers that cost less than half now.
- The quality is whatever you print. The printer's quality is stellar.
  
  I always say that if you want to print stuff, buy Prusa. If you want to tinker with the printer, buy something else.
  
  Prusa is the Mercedes of 3d - premium price for a premium experience. At 100$ for a Mini, I would not hesitate even if I already have one.
- The print quality is fine if the printer doesn't freeze. Nothing exciting but also not bad for a $100 used device. Still, nothing to ride home about if $200 buys you a new BambuLab A1 mini. In sharp contrast is the Bambulab a reliable and superior printer in every aspect.
  
  With this sad. If you still consider the Prusa Mini:
  
  DO NOT update the firmware to versions with input shaping! They introduced a bug that you need to remove the SD-card before turning it on or otherwise the printer believes the firmware is damaged/bricked. This bug has been known for quite a long time without any fix from Prusa (present in multiple "stable"/release firmware versions!!!). I got rid of the last Prusa few years ago because of this issue so it might be fixed, might be still broken.
  
  Do not rely on network connectivity/features. They are unstable meaning the printer needs to be restarted multiple times per day (combine this with the SD-card issue) and might freeze mid-print.

If it works, it's a superb deal. And the print area will probably cover 80% of everything you might ever print.

Edit: Print quality is more about your ability to tune your printer, no matter the brand, then it is about the printer brand itself.

As someone that has one, I'd say more than 80%. That might be accurate if you only print other peoples' designs, but for functional parts I've designed, 80% are a total non-issue, 10% need to be rotated 45 degrees on the build plate, 5% need minor redesign to fit, and the rest I was able to break into multiple prints without issue.

Even if you eventually need a bigger printer, I'd still buy this one. I've definitely run into situations where I need to print multiples more often than I've wanted to print something big.
- Yeah, it could be possible to only ever need the mini and 80% is perhaps conservative. But, I as much as I find my Bambu Mini can cover the majority of my printing needs these days, I still need the print volume my Prusa Mk3s has for a very good number of practical prints I design and print. The real world often demands real world size and hates pieced together part designs lack of strength. And I still often need to resort to my metal working shop with lathe, mill, drill press and welders to make serious parts because plastic just ain't it.

That's apparently a $400+ printer new, so yes, I'd say $100 for it is a good deal.

That said, Prusas in general have always been too rich for my blood; my idea of a "good" printer is a Creality Ender 3 V3 SE that I got as an open-box for $150. I'd probably still take that over a Prusa Mini because the print volume is bigger, but the low price you found would definitely get me considering the smaller printer.

If you are oke with the smaller volume, this is a good printer. this thing will be able to print flawlessly, all parts are semi open source and there's a great community if you need support parts or any help. Prusa is above average stuff.

@elcroqueta It is quite a good deal.
And a good printer also.