How about a moderately fast used P3 or P4 laptop? Bob Johnson.com has some pretty good deals. And if we happen to own something better (I'm using the group 'We' as I doubt that I'll be attending), we can always give it to a kid or a charity.

Until it lost half of its memory, I had a ThinkPad T23 running XP Pro, SQL Server 2000/2005 (depending on when) on 256 meg of ram and it was pretty responsive.