Other points to remember if you bring machining in house is that whatever machine/s you have, it / they have to earn their keep: if you suddenly have a quiet period, have you got other work you can put on the machine? If not, it could suddenly become an expensive liability; you'll still have rent / rates to pay on the workshop space (have you a workshop at present, or are you working on the designs at home?) , service supplies for it (electric / heating / air / water, dust extraction and waste disposal charges), materials, labour (your biggest cost), equipment costs (machine itself has to be paid for, tooling, clamping / fixture systems, maintenance of machinery, gauges and test gear) - these all have to be paid whether the work is there or not.

Bear in mind also that if you don't know how to use / run that machine, you need to employ someone that does, otherwise you make nothing at all and you end up with customers frustrated with delays (they themselves may have customers waiting for a finished item) whilst you figure the machine out - it's not impossible that a customer ends up going elsewhere if you keep them hanging around for parts.

I'm not saying don't do it, but you do need to consider your costs (and implications) extremely carefully: it may appear at first glance that doing your own machining will save money - but if you lose customers through delays / damaged items etc, or you find times are tight because there's no work to put on the machine, it may well be that subbing it out is actually more cost-effective.

FWIW, the Proto Trak CNC systems may be useful to you - they are specifically designed for one-off / short runs and are easily and quickly programmed from job-to-job (look up South Western Industries, or XYZ Machine Tools in UK / Europe) if you do bring it in-house.

Hope that helps.