I am a new owner of a 1973 31'. I just bought a Prodigy a couple of weeks back. There are two internet places that have better pricing that what has been mentioned so-far. Check out these two web-sites:
Prodigy on sale for $98.99
sale for $105.00
I bought at the second site since they happen to be just down the road from me (I am in Portland, OR) and the shipping cost from the other site made the difference about a wash. The special connection pigtails are about $9.00. I installed mine in our 2002 Dodge Ram 1500
using the pigtail that I received with the truck (the truck came with the trailer towing option package and the pigtail). I spent a total of about 1 hour but that was mostly because of the location I decided to mount the unit and the fact that I needed to drill a hole in the panel below the steering wheel to get the wire out of site faster. The installation directions were pretty clear with enough information to connect up even if you do not already have a built in jack. I bought some crimp connectors to connect to my pigtail and found they were allready included in the box.
I do not yet have much experience with the unit but it seemd to work fine when I towed the 31' home from where we bought it.