Well first off would be to determine if the cruise wiring is already in the car, my EF GLi lacks the wiring due to not having ABS, but an XR may already have it.
depending on where u get parts from, i've seena wrecker selling cruise control 'kits' for $100 or so, but that was a self serve wrecker.
checkout
www.fordmods.com for a full tutorial on installing cruise.