Shay Howe is a person that speaks my language. I am a trained auto tech, have worked as a motorcycle tech, and worked on turbines all in a past life when I was younger. Tinkering is what I do in my spare time. I suggest going down the used bike road. If you go vintage disc brakes will not be an option, but the price can be very agreeable.
Example: I have a 1985 Miyata Ridge Runner, a top of the line bike in 1985. It is sporting a riser stem, cruiser handle bar, big ol' Cloud 9 saddle, and a 6 speed drive train. I converted it from a mountain bike to a simple 6 gear cruiser all with used parts. Nothing near as complex as anything automotive, but fun to do, and even more fun to ride.
One thing about disc brakes you need to know. Cheap disc brakes are nothing more than BS. They don't work any better than rim brakes, are consistantly frustrating to work on, and are not worth considering. I consider them the Yugo of brakes.