I just bought a used one, old style made in 1989. I paid $475 w/o tax. You could get it cheaper even with shipping from an internet place like KY Imports or JG Sales, but you wouldn't get to handle it first. Guess it depends on how soon you gotta have one.
I love mine, couldn't be happier. The only bad thing I can find about it is the somewhat thin blue finish and tendency to rust--it rusted a tad when I was in Missouri this weekend. In all other things--trigger, sights, accuracy, recoil, comfort, pointing, simplicity, and reliability--it exceeded my expectations. I love it.
Comparison to Ruger is not quite fair to the Ruger, IMHO. The SIG is a different class of gun altogether. I actually like the Rugers though I have little experience with them, but I wouldn't compare one to my beloved SIG.