I've done plenty of 3 deck mixes with final scratch. Its got a really decent loop function as well - so you could load up a loop onto the third deck and it will loop away. To make it even easier you can set the third deck as a slave to the first or second decks, and it will keep in time. Gives you more time to do more interesting things...WTF!
What would it cost me all in all?
FS and latest Traktor that is.
Have a look about on ebay - you could get the full version of Traktor 3 and FS2 for around £350 all in.