Used to buy second hand/reconditioned laptops, but these days you should be able to get a brand new laptop within your price range.
Two things to watch for - does it come with the original battery or a new battery? A two-year old battery will have a lot less life than the original battery.
The other thing I've noticed is that the screen brightness always seems to be a lot lower on a second hand laptop -though I suspect that's a function of age. If you can pick up an "open box" model (ie. one that has been returned to the retailer or manufacturer soon after purchase), then the above two points may not apply.
Also - have you considered a Netbook? I am well pleased with my Asus 904HD which I bought in February: 1Mb RAM (which I quickly upgraded to 2Mb), 80Gb HDD, XP and Open Office already installed. Only slight disadvantage is screen resolution (1024 X 600) - so bit more up and down scrolling. But weighs only 1.3Kg and runs for about six hours before needing recharging. Paid about £330 for mine.