I'm sure that bike is worth that price to somebody, but it wouldn't be to me. I do like the fact it is a vintage track bike and appears to be in very good shape. I'd want a peek behind that tape on the top tube to ensure it isn't covering up a nice dent. It surely had drops on it originally and they may have caused damage there. Not a deal-breaker, but something good to know. For some it might be a deal-breaker though.
I like your idea of building up your own.