I really think 72" fixtures are overpriced. 3x250w retro kits cost about $600-650 with the option to chose the bulb of your choice (usually plus/minus $5-30 depending on bulb cost). I think I'd just build or have a canopy built with the money I would have spent on a fixture. even cooler would be to hang three pendants. that would add about $100 per retro kit for the fancy reflector pendant but its still cheaper than most fixtures.
but if thats not an option or you want a fixture how much do you care about the fixture having supplemental actinics?