I was mildly disappointed with Vavles pricing, so I told my nephew i'd make him a Bazzite system. He plays simple games.
Specs: Ryzen 4650G 450W PSU B550 Asrock ITX board 16GB DDR4 @3600MT/s 1TB PCI-e 3.0 Nvme Coolermaster 240 AIO (somehow crammed in) Silverstone SG-13 case
It was $540. But admittedly, the ram came before the AI apocalypse. So it's probably closer to $700 now. All off ebay, except the case & PSU.
edit
Missed you comment on the performance difference to the steambox. It's bad. The 4650G isn't great. Played deep rock galactic at maybe 45 FPS.
I haven't done benchmarks, but it's about the speed of a GTX 1650, but being AMD it works much better on Bazzite (Linux)
double edit
I have about 10 nvme drives of varying sizes from before. The 1TB drive cost me $70 (about $78 after tax) before the shitstorm.