Moped Army

Im helping my buddy find a moped and i came across a 1977 Bianchi Snark. Its not a pretty site but it does have a title. It has a minarelli V1 motor but needs piston and rings. I can get it for 200.....is it a good buy?....ill probably end up buying a new kit for it, and everything that matches. im guessing $400 or $500 put more into it when its all said and done.....at what point am i putting too much into it?