Is there any guidance in the books, or from the FFG devs, on what it would cost in credits to add a basic workshop to a ship? And what the cost of some of the advanced benefits might be?

The colonist book has a workshop cost for the ground or space station. That's as as we get as far as I am aware.

Thanks! I'll give it a look. It's a starting point at least.

Special Mods reccomends it be a big reward or purchased with Obligation.

It mentioned the cost being "tens of thousands of credits" so if you need to put a credit amount on it you can assume a minimum of 20,000.

Likewise advanced benefits are suggested to be rewards.