You might be better off, and have considerably more luck, finding a working D50
secondhand, transplant the motherboard if you like to bring your original one back to
life, and sell off what's left as spares (you might actually do alright out of that). I
picked up a D-50 last year for £160 - a bit beat up, but functionally intact. I'd be very
surprised if you could get a tech to fix it for less than that, especially if there is
no-one local to you.
Incidentally, if you do go this route, and end up with a
spare pitch wheel, let me know... :-)