Buy 2 BEHRINGER UCA 202..(http://www.imuso.co.uk/ProductDetail.as ... de=ST00501)
20 quid Each=40 QUID

These basically are the same as ...

And you would need to buy 2 TIME CODED VINYLS(10-15quid eac) to put on your decks.

And rest is fairly simple
Plug out outputs both of the usb sounds cards.. in to channel 1 and 2 on ur mixer
and then RCA cables from decks to the input of each soundcard
Only Disadvantage with this is you would need a program which LETS YOUR CHOOSE YOUR SOUNDCARDS(which Serato,Torq dont let you do as they are specifically designed to be used with there special hardware)l
You would need to use software such as Numark Cue( Aka Virtual Dj) To be able to scratch your MP3.
I would recommend this to be a home set up and wouldn't recommend people taking a setup like this to a club but it is perfect for practice