Windows machines don't depreciate
that quickly that you'll be able to find a "high end" laptop in that range, unless it was "high end" 3-5 years ago (maybe).
And with something that cheap and that old (Windows or Mac), I would be worried about the condition of the laptop and whether it would really be worth buying.
Honestly, 30seconds of searching brought me to an HP model with an i3 processor, 4GB RAM and 500 GB 5400rpm HD for $450 brand new. I'm sure with a deal site or actual research could find something even cheaper or more powerful (i5 maybe) with the same price.
Honestly, you could get a
HP Pavillion dv6t Quad Series with a similar 2.2 GHz i7 Quad Core processor, double the RAM (8GB vs 4), 250 GB more HD space but only a 1366x768 screen for $905. Make it a 1920x1028 screen and that is $1055. Almost $800 less than the base line 15" MBP stuck with a 1440x900 display. Highest you can up the MBP display is 1680x1050, for another $100-150.
There's a lot of options out there for a Windows computer in terms of pricing and specs. Just look around.