As others have mentioned, you need more definition and probably experienced help. I agree with the previous comments that $20 is the right ballpark for the electronics but it could be $30 easily and much more with poor design. Not included in that price is the enclosure. A basic off the shelf plastic enclosure is only a dollar or two, but drilling / milling holes and labels add cost very quickly. A custom enclosure can be cheap, but there may be hundreds or thousands of dollars in tooling charges. The biggest risk with jumping into medium volume production is probably warranty / reliability.
Steve