So sorry to hear of your resent finding of the rust. I don't know what region you're in, but rust is common in the "rust belt", north central area and toward the east coast where they salt the roads. You said the rust was on the frame, but our cars technically don't have a frame. They are "unibodies", meaning they are a single molded unit forming both the bodywork and chassis of the car. I don't want to scare you, but your comment "what you don't know won't hurt you" might not be so. Depending on the location and severity of the rust, it compromises the integrity of the structure and areas that might support the suspension. If the metal is fatigued by rust it could give way while you're driving down the road at 60 mph which could be catastrophic. Certain counties or states in the east require a periodic safety inspection and mandate the rust be repaired if it's deemed unsafe.
IMHO, I would not put any more money into the car than necessary to keep it rolling until you find a replacement. Just my oppinion.

Good luck