Data point: I have been doing exactly this with a X3430 45nm system for over a decade. Old Xenon systems are very power hungry compared to modern servers. Expec

Data point: I have been doing exactly this with a X3430 45nm system for over a decade. Old Xenon systems are very power hungry compared to modern servers. Expect to pay tens of dollars per month if you want 24h uptime. I just checked the Kill-A-Watt behind the UPS and it's reading 170KWh for 2054 hours. I'll leave the exercise of determining if this is cheap or expensive to the reader.