I purchased an Acer 15.6", i5 Win8 laptop with 12Gb RAM (came with 6gb, added another 6gb for £18.99) and 750gb storage for a shade under £450 ($730) in one of the end-of-summer deals.
It runs Traktor Scratch Pro flawlessly on the lowest latency settings, and has a sub 5-second boot up time (this still amazes me each time I turn it on- but then I am easily impressed…).
The only ‘optimisation’ stuff I did was turning off all the power-save/sleep functions and disabling the auto-update for Windows & Anti-virus. I also uninstalled the couple of useless media programs that come installed on new machines.
I also have the wireless internet connection off while I use it for DJing.
If the laptop is going to be used for other resource intense applications beyond Traktor then by all means go for the best spec you can afford in budget, but if it’s just for Traktor (as mine is) I would be tempted to take Makar’s suggestion.