need to know how tall it is so you can make sure you have enough light to hit teh bottom.
a 48" T5 fixture with 6 bulbs would do you well up to 24" deep. they are about $500 depending on what make/model you choose. i have seen a few 48" on here for sale, not sure if they are still avail.
If you are looking to build or retro it, it will cost less, just not sure how much