I set up one of my current activities based on outsourcing as many parts as possible, in stainless steel sheet and various plastics.
I also do limited numbers and two to three years in I realised that a small cnc might help me.

In the end it turned out to work better if I tried to make as many parts myself as I could.
I think that if you want to do custom work, having your own cnc is very useful.

If you need to start by outsourcing, which is a good idea, even if doing parts yourself is "better" in the long run, the supplier needs to be flexible too. That probably means that they are focusted on small batches too.

Mixing small batches with very big ones is often hard, unless the business actually focuses on being able to handle both.

Having a local one may be very good. Being able to just pop over to discuss stuff makes stuff much easier.

I think price will come from how much hassle you take out of the job.
If you can send nested cad files or even coded files to the cnc guy that only need cutting, it would be a lot cheaper than sending each individual part file over, adding quantity, thickness.