Just for the record, if it is a 79, then there are a lot of things that you are gonna want to change if you get it. You will want to replace the front calipers with ones from an 80, as the 79 used a wedge design that is very prone to failure. You cannot use brake parts from 81-85, as they use a different thread pitch on the lines. Also, you will want to pilfer the electric ignition of the newer 1st gens. On this, you would preferably use the ignition from an 81-85. While the 80 is electric ignition, it uses ignitors that fail more frequently and are much harder to come by. The stock 79 ignition is still a points setup... If you can find one in a junkyard nearby, pull the rear out of an 81-82 GSL model to get rear disc brakes and a clutch type LSD. It is a bolt in swap but will require you to pull the back part of the ebrake cables and getting either a custom soft brakeline from the chassis line to the rear, or you could just buy the stainless line kit from Mazdatrix which can be ordered to facilitate the swap.
One good thing is that the 79 has the best flowing intake manifold due to the least amount of emissions control crap. The car can make good power once the thermal reactor is ditched in favor of a good RB header and presilencer.
How much to pay is really gonna be a matter of condition and how badly they want to move it. I paid $100 for my 80. It had sat for 3 years due to what had been diagnosed by a boinger mechanic as a blown engine. The owners were about to have it picked up by a salvage yard. It only had 52000 miles on it, and incidentally, was only flooded. You need to learn about MMO. It is your friend. Post or PM any specific questions you have and I will try to help you.
One last note, beware of rust in the rear wheel wells that travels into what would be the package bin area of the later cars, but is dead space in the 79 and 80. It is a major problem area that you should be aware of...
Good luck,
James