NeedABike23

Hi, Total Newbie here looking for advice. I've been wanting to buy and build a bike for as long as I can remember. I'm thinking a cross between a cafe, bobber, and definitely all rat. I guess this inspiration was sparked the first time I watched Mad Max and furthered by my brother's recent aquisition of an old CB550 for $50. Anyway, I've found a '74 RD200 on craigslist for $450 that I think I can get it for $300 since it's not titled. Is it worth it? I want to use it to get to work and to just have some overall fun messin with/ riding it. My commute is 40 mi 1 way so gas mileage is a concern. But since I'm currently putting over $100 weekly in the tank of my Jeep anything would be an improvement. I've heard 2 strokes can give similar power to 4s with smaller engines, but I don't know how this effects fuel consumption. Another consideration is this, or any, bike will be a project to work on with my son. So again I ask, is it worth it or should I keep looking?