I would like to build a budget unraid server build from 100 to 500.

I would like to use it for a nas, vms, maybe plex

I need a motherboard, CPU, hard drives, preferably a 2u server chassis

Are you talking US dollars? Even without disks that budget seems tight. 

Do you have any components now?  Otherwise, used is the only way I can see pulling that off.

I do have a power supply but that's all 

I have changed my budget to $700

Yes US dollars

 

Pick your compromise...

 

You can look for a used server. As long as you are in a major market, you should be able to find something. It will be old, but functional and cover everything you've listed.

 

You can buy new-,ish and plan for growth. Ryzen is a good value. You can pick up a 1000 series CPU fur a good price and pair it with a higher end board to gain compatibility as you acquire more powerful versions. A minimum of RAM, like a single 8gb stick, and a couple 1tb drives.

 

You would be able to do a coupe of Dockers and Nas with no issues. Light VM potential. Best of all the foundation parts can support more ( better CPU, memory, GPU, drives,).