Andy,
Yes Halides would be your best option. Even at 2W per gallon it will be tough to get the carpet look your would like to go for. Tall tanks are not ideal for carpets though some mosses might work. Hemianthus Calllitrichoides, Micro swords, dwarf hair grass and other popular carpet plants require high light of 3-4 watts per gallon. Also remember the higher the wattage the larger the need for Co2 injection.
Personally I would pick the plants you want and design the lights and system around it. It avoids spending extra money on upgrades in the future. I would go to plantedtank.net and research some of the members aquriums and what plants appeal to you before spending your $ on lights, substrate, etc.
Regarding cost effective lights, ahsupply.com has great lights and is used frequently on plantedtank.net. Note some
DIY knowledge may be useful if you go this route.