A Dell R230 on Xbyte shows $599 to start.
"To start"...in that case it's without CPU, memory or disk. So it's a server that does not start.
Get a new one instead from Dell. Dell R240, 8GB ECC RAM, Dual-core G4900 CPU, 1TB disk. $709 ready to go on dell.com
G4900 is latest gen CPU, more than you need. To step up to 4 cores it's $176 to get a Xeon E-series CPU in the same machine.
Supermicro is never going to be a cheap as Dell or HP low end models so there's no point even looking at it.
PS. Also you get 1 year basic HW warranty on site in that price but you could extend to 3 year for $100 or whatever the customer wants.