If the frame is really something special it might be worth considering. If the rust is only on the surface, it can be easily removed either by sandblasting or with sandpaper. The problem is if th rust is inside the frame (and it usually is in older steel frames - soetimes just humidity will be enough to roun the frame over long time). If you're using sandpaper bear in mind that it'll take you a long time to get rid of the paint andthe primer. Some sports might be extremely hard to reach, so I think that sandblasting is a better idea. If you can combine sandblasting and painting together, the whole thing should cost less than if you do them separately. In any event, as I said if it is really great frame, worth restoring, go for it. Otherwise, forget about it.