You can get a new radiator for ~$350.
E.g. [link|http://www.auto-car-radiators.com/cgi-bin/webc.cgi/st_prod.html?p_prodid=13493&p_catid=508|Here]. Plus shipping, I assume. Your local autoparts store (e.g. NAPA) should be able to get it too.
I don't understand why it's so expensive in the quotes you were given. It should be trivial to change (it usually is on a 1960s V-8 American car). The hoses should be easily available too.
But if you need to pay someone to do it, you'll have to pay what they want to charge. Labor is ~$60 - ~$80 per hour around here, and 2 hours isn't unreasonable (some of the bolts might be rusty).
The thermostat should be about $5. It should be easy to install too (maybe 30 minutes including cleaning things up, etc.) unless it's really hidden away somewhere. You should generally replace the thermostat when work like this is done.
Should you do it? It sounds like the only thing you can do is fix it if you want to have transportation (other than a cab or bus). If it was me: if the car is OK otherwise I would fix it.
You can sometimes find a decent car for $800, but it might need $250 for tires, $250 for brakes, $250 for ... Ask Box. :-(
Luck!
Cheers,
Scott.
