Personally, I would place a cap of ~$150 on a driver. Since you have capped your amp price at the same, that leaves $200. So, $100 for a good quality box and $100 for install and cabling.
Parts Express has a couple of good sounding units that are worth looking at:
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=295-464
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=295-404
Concentrate on getting a clean sounding amp stable at 4 Ohms and you're good to go //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif