We would need more info, such as who the provider is, if it will be managed, things like that. I have seen similar configs go from $80 per month to $300 per month and up depending on the provider and add on services.
It really depends on what its worth for the client. What kind of parts do you use for the server? Desktop parts? Server parts like ECC ram, etc, you posted that already but not other things like disk brands, models, speeds, etc.. What kind of network guarantees you give on packet delivery and SLA? Is it a dedicated port fully unmetered or shared? What kind of managed services comes with it? What kind of support comes with it? You see someone could pay 100$ or 500$, depending on what value it gives to the client.