Cheapest option I found when looking around for a new computer was to use my existing monitor with a 'net-top' - similar spec to a netbook, but you're not paying for a screen so it's half the price.

But, if you decide on a laptop, it should have USB sockets, and depending on the type of hard drive you can either borrow a widget I have that plugs IDE into USB and powers old hard drive from plug socket, or buy something similar for £10-20 or so to get data off old hard drive and onto laptop (or even use old hard drive as an external backup drive, like I do - when I remember).