Really need some pictures to assess.
A car that can't be test driven is dicey at best. Could be a clutch cable but the transmission could also be garbage. Clutch could be shot. Clutch could be frozen to the flywheel. No way to know unless you can drive it.
Since you can't drive it, you can't assess the brakes nor can you really assess the engine. An engine that idles doesn't guarantee an engine that has power under load.
I'm always suspicious of a seller that won't take the time to fix something simple like a $30 clutch cable to improve the sale-ability of the vehicle.
There is always more rust than whatever you can see.
Without more pictures or more detailed descriptions of the car's issues I'd say you're looking at a $1000 car. Tops. Could be parts only if the rust is bad.
Scour this site. Lots of information on what to look for when buying. Always buy the best car you can afford. It's far easier than buying a fix-er-upper.