I have an Antec something-500 from 15 years ago and a Caselabs ITX case that is larger (for custom cooling, etc - I never did use the space) and in 2018 transplanted the guts into a SFF from Sliger and I could fit four of my new case into the Caselabs case - and they are commanding quite the premium in the afterlife.
Height and Width are less than my MacBook Pro (deeper of course but still only 13.5cm)
I don't compromise on much, sure there's only a single PCIe slot but it's got a full size GPU in it (rx5700 reference design), a 650W Gold modular (SFX) power supply. RAM is 16G (lots for my use case - the MB is 2015, not sure it supports more - but with 64G sticks I don't think two slots is much of a limit), a M2 PCIe drive and a separate 2.5" SSD, two Noctua 120mm case fans and a decent after market CPU cooler. It's quiet and it runs cool.
Lastly on price. A good quality power supply is going to run you 150-200 and most decent cases are in the 150-200 range without a power supply anyways. These are small run manufacturers too so that makes them pricy too, but they'll last 5-10 years (eg a couple of MB upgrades) so worth the investment to some.
They are a pain in the ass to build in though :). (The Ghost looks a bit easier but wasn't really available at the time)