Believe it or not, JC WHitney has a kit with an electronic actuator for under $300. You'll probably need the electronic actuator because most cruise controls work with a vacuum actuator... and with the turbo there is sometimes pressure, not vacuum, so the vac actuator won't work.
Unless, that is, anyone has tried it with a vacuum reservoir and a one-way valve and found that it works...
Let me know! As far as I know, nobody has installed a cruise - YET - but it's just a matter of time for me. My thought would be to use the switches from a P5 (steering wheel mount) with an Audiovox (or other) electronics box and elecrtonic actuator. Should be fairly straightforward, just time-consuming.