Build configuration suggestions for a budget, in-home NAS system

I'm a single developer who would like to build an in-home NAS system that I can store my code repositories on. It doesn't need to be anything special since I would primarily just be using it for storing repositories so I can access them from multiple computers. I would like to stay under a budget of $150 if possible so if anyone had any suggestions on cheap mini-atx cases and things like that it would be very helpful. My thoughts are as follows:

CPU: some older single or dual-core CPU for processing
Case: as stated a mini-atx case would be preferable to save room. Biggest issue would be finding one with a resonble drive bay setup to hold one 3.5 inch drive without much hassle.
Power Supply: Not quite sure what I would need exactly considering this build shouldn't consume too much power. Though I would probably won't a gold-certified one
Motherboard: I would imagine I wouldn't need anything too fancy here.
Storage: given this project's purpose an enterprise style drive might be good but not sure what will fit into budget.

Thanks for any help!