Decided I needed to replace my rather worn tapes with some shiny new CD's and found that Play.com are doing the special editions of the first 2 for £9.99 each, next best was £12.41 each at Sprint Books. Each series has been remastered and includes lengthy interviews with Douglas Adams.
For those of you not aware The Hitchhiker's Guide To The Galaxy started out life as a radio series, the first 2 series (now called the Primary and Secondary phases) were produced prior to the books. After Adams death radio adaptations of the final 3 series were produced reuniting most of the original cast.
If you've never heard the radio series now is a good time to start, the Primary Phase was recently voted Britain's favourite Audiobook for good reason.
Don't forget Quidco ;-)