Most of the LFS in town have competitive pricing on lighting. You can save a bit of $ by shopping online if you choose, but you'll miss out on meeting and dealing with some very nice, very helpful people in our LFS owners and staffs.
One of the easiest and most affordable way to upgrade your lighting is to go with VHO. You can put 440 watts of VHO over your tank which will allow you to keep all but the most light-hungry sps out there, (but that's a matter of much debate). An IceCap 660 ballast will cost about $170+/-. End caps and bulbs vary greatly in cost, but a setup of 4-110W bulbs with endcaps should run you in the neighborhood of $150-$180. Drop these into a DIY canopy and you have a great light setup for under $350.
There are other ways to go, certainly. This is just my suggestion. Good luck.