what are they worth
Sadly, Porsche 914 = RUST. Price will depend on the amount of rust in critical points (around engine, floor and suspension) overall conditions of brakes, transmission, and interiors. I would pay $5K to $7K for a VERY good conditions one.
those are the main rust spots of these, id say around 2k maybe, if it runs and everything, you can put all new sheet metal in to fix this though, and make it worth around 4 or 5k