Look for a secondhand server from a recycler or ebay.
Decent ne 'Low Cost'
There's truck loads so hard to advise - a lot will depend on budget & real world usage.
Check HP ML towers or DL racks, and similar from Dell. Usually all RH compatible.
I suggest you really spend some time reading up on hardware - there is plenty of info on CPUs, RAM, HDDs, Raid cards etc. so you really understand what you need, and can spot a good deal.
I still run a ebay DL380G7 at home. Truck loads of RAM when bought & slapped a pile of new drives in. Runs Proxmox, SME in a vm plus other vms too.
You will find cheaper, but you get what you pay for. Less flexibility, upgradeability, power etc.