Eh, maybe a bit when compared to a NUC, but I'd not say insane. It's not possible to do a direct comparison, but this is what I came up with:
NUC BOXNUC8i5BEK1: $390
(Went with the i5 NUC because the
i3 is only dual core. The Mini's CPU still is much faster at base but can't quite match the NUC's turbo (
on two cores, on four they're even). The NUC's iGPU is appears to be better though. Its CPU also has hyperthreading and probably more L3 cache.)
Crucial CT2K4G4SFS824A 4GB x2: $70
(NUCs use DDR4-2400, the Mini accepts DDR4-2666.)
Corsair Force MP500 128GB: $100
(Assuming here that the Mini is using the equivalent of a NVMe MLC SSD (we know it's PCIe). Apple always over-specs the SSD even where a SATA unit would be just fine.)
Windows 10 Home: $99
(Yeah yeah, Linux. But the Mini includes a commercially supported OS, and Windows is the closest match to it. One could also argue that Win10 Pro, at +$50, is a closer match to macOS.)
Total: $659
So, $140 cheaper (the base Mini is $799). Not great, but could be worse. I'd bet that willingness to go mITX over NUC would increase that difference some.
Other Mini advantages/drawbacks:
+ +3 Thunderbolt 3 (this is probably a big chuck of the premium $ right here)
+ DisplayPort 1.4 (1.3?) (5k display support)
+ +1 external USB 3
+ Expandable to 64GB RAM
+ Built-in PSU
+ Support for up to 3 displays
+ Aluminum case
- Non-upgradeable SSD
- Seriously, soldered-in SSD
- 1 year warranty
- Size
Other NUC advantages/drawbacks:
+ Upgradeable SSD
+ Size
+ External microSD slot
+ 3 year warranty
- Limited to 32 GB RAM
- Only a single TB3 port (that could be eaten by a DisplayPort monitor)
- DisplayPort 1.2
- Supports 2 displays max (Intel's spec page says 3, but there's only one each of HDMI and TB3/DisplayPort)
- External power brick
- Plastic case
So the Mac tax is there, but it's hardly so egregious at least in the base config. Especially when you consider its base CPU speed and additional TB3/DP ports. It really does come out though once you start upgrading the Mini's SSD (at least RAM can be bought aftermarket). Though you could probably say much the same about any other OEM's upgrade pricing.