Fast Ratio Box Value?

How much do you know about the seller? Sounds to me like he doesn't know what he has (just a steering box off an old car) and is fishing for a value. If that is the case, I would offer him $25 to start and work from there. I've recently bought steering boxes for that. If you start out too high you run the risk of the seller deciding to sit on it in the hopes that it will be worth even more later. If he/she is offended, you can always offer more money. Just my $.02.