Has anyone ever installed one of the RKE systems in an older car...like a 75 CDV? If so how hard was it and did you use one of the $50 specials from the Autozone or some expensive model?

I installed a GM system in my Impala SS. It already had RKE, but it takes the place of that and adds an alarm. It is the "VSC 3100". It has worked flawlessly for over five years. GM doesn't make them, but whoever does does a good job...

My thing is, i don't even know where to begin. Are the instructions on these things that intuitive?

Yes, the instructions are good. However, if you don't like being upside down under your dash cutting and splicing wires for an entire day, let a shop do it. Places that do alarms know the colour codes off by heart, and they know all the tricks to work fast. When you find out what the install cost is, you will think, "wow, I can't believe I was going to do it myself!"