Hi, Mark -
$300 sounds pretty good. I'm pretty sure the difference in windshields is one fits all hardtops and convertibles, and another with slightly different dimensions fits all 2- and 4-door sedans and station wagons. Also, I believe they interchange between GM makes for 1959 and 1960 with some exceptions on Cadillac.
I know of at least three classic glass manufacturers who make glass for these cars - one I have spoken to is Bob's Classic Auto Glass in Blachly, Oregon - (800) 624-2130. I talked to him a while back about complete sets for a couple of cars I will be restoring in years to come. I think his windshields are more expensive, but he makes all of it including rear glass, in clear and a couple of different tints. He was the one who filled me in on interchange, and apparently the fact that these also fit Chevy and others means there is a larger market and is why they are available in reproduction. I can dig up a couple more sources if you need them - I seem to remember there is one in Georgia who usually has a booth at the Tri-State Swap Meet in Denver every February.
Is this the same car you were talking about being a factory A/C car but missing some components? If so, as someone said, that is a rare option - you may want to consider leaving everything in place and keeping an eye out for the missing pieces over time to get that working later. It will increase the value of the car and keep a rare one together.
Now go buy it before I come looking for it (I have too many already!!)
- Doug