One more vote for the NUC. I have two, a Hades Canyon (high end) and an older smaller form factor one. You can find fully configured units for less than $600 new, probably half that used. The entire unit is 4 inches square and can be mounted on the back of a monitor or operated headless remotely.
I run upwards of 20 instances of ProScan, 4 of PRO96Com and a RadarBox all off the NUC with 16GB of RAM and a 1TB SSD, total investment under $700 for the NUC, RAM and SSD.
The Hades Canyon is more expensive starting at about $1000 but are more geared toward the gaming crowd. I have switched to using it since it supports up to 6 monitors at 4K, I needed 3 and the little NUC only supported 2. In this one I have 32GB of RAM and a 2TB SSD, it runs all this stuff and I am using 3 monitors and it doesn't even break a sweat.
If you buy new Intel support is great, they come with a 3-year warranty. You can save money and buy it as a kit, with no RAM or storage and add that yourself.