Tricky, unless you have a 6' x 5' slot and 3 phase because old Bridgeport Interacts are currently going at bargain basement prices.

If someone else takes a hobby mill, fits ball screws and stepper motors the price seems to take an unreasonable leap which is why most of us do the conversion ourselves. Basically you buy a mill then use it to cut the plates and stuff required to fit the motors. Then you start CNC'ing and soon decide to make them all again because you can now do it so much better.

How big are these sprockets? You will need to ensure you have enough movement on the Y axis to handle it. ie: Max diameter plus tool diameter plus a bit for setting up.