Call your local lighting rep and ask for a quote. If you are doing a decent quantity, you should get some good prices and they can help you with the specifics of what kind of fixture and lumen output you are looking for, and what the best bang for your buck might be.
T5 fluorescents are great, in the right situation. Don't expect long life out of the lamps and ballasts if the temperature of the area they are in isn't well controlled. They simply will not last in high temp applications where it reaches 85ºF+. I have hundreds of them in a distribution warehouse and they were great at replacing MH fixtures but it is climate controlled @ 75ºF year-round. The rep told me up front about the operating temp limits of the T5 fixtures.
ITO, I would agree with the idea of talking to a lighting rep. That's all these guys do, is specify and sell lighting products. A few years back I needed to get some sort of an installation underway for a boning room at the local meat-works, I sort of knew what we would need, but I went and saw one of our lighting guys and he came out and measured up the building and then gave me a really professional print-out with various options and a plan of what the lighting levels would be in the room itself given a particular type of fitting. To say the least, I was really impressed. We made quite a bit of money on that job, and we ensured compliance with the various Health and Safety regs and the MAF regs in one fowl swoop. In regards to the original post here, I would seriously look at T5 fittings, bearing in mind the comments of Fred above, T5 fluoro's do not like wide temperature variations, the thinner tubes being the main reason for the variations in light output. T5 fittings exclusively use HF ballasts, which means that there is no strobo-scopic effect around rotating machinery, often found with T8 fittings that use wire-wound ballasts. Just my $0.02 worth.