I'd 2nd the Kmart kits.
Get one on one of their 20-25% off days & it will be a lot less than $200.
I've used them for over 10 years now with no major problems. The odd dirty contact has stopped them from time to time but nothing major.
As Matbor says, try & get an electric actuator if at all possible. I haven't seen them available in DIY kits though.
I've found that as the engine loses vacuum up long hills (do to wider throttle opening), the cruise loses vacuum & won't hold the throttle open as far. An electric actuator would alleviate this problem.
Another option is to use an electric vacuum pump to operate the vacuum actuator but this is probably complicating things (although the Discos use one for the factory cruise control system).
I wouldn't have a car now without cruise control. All of my regularly driven cars have the Kmart kit fitted :) .
