That is high. I own a 1986 R300 Cannondale, I was the original owner, sold it, after two other owners I got it back. back then the model numbers actually denoted Price. Hence R300 was 300.00. I'd check around ebay, or craigs list (not SF). mine is 53cm, But you can find something cheaper, just make sure that it is in good working condition. What ever used bike you buy, check it out for fit. Also the classics forum is a great resource for parts, information.
You might be better buying new lower end road bike, unless you enjoy fixing up old bikes. It is a labor of love, but from a financial standpoint, it may not make sense. Happy Hunting!