I think it would be worth a try to grow purple prickly pear in your Florida sand. If anything would bother the plant, it may be the salt content, or possibly the high humidity in Florida. They're tough plants, though. They'll be most purple in full sun and under water stress. One word of advice--the glochids on the plant can go airborne with disturbance (say you drop a pad or sneeze too close to it), so handle the cactus even more gently than you usually would a cactus.

The purple optunia 'Santa Rita', is reported to grow naturally in AZ, NM, TX, and Sonora Mexico. So I don't think it only grows in AZ sand. Get some builder's sand from HD or somewhere and mix 2 parts sand, 1 part potting mix. Grow it in an area with an overhang if you get a lot of rain or dew where you live. You can grow it in a clay pot to further prevent root rot or put it on a slope or hill to help with drainage. I used to grow cactus in Louisiana that way and as long as you can keep them dry they should be okay.
~SJN

After reading your messages, I have decided to try growing the santa rita in a pot. I have ordered a 5 gallon plant, supposedly 1 1/2 to 2 feet tall. Being a snow bird in Florida, I will be leaving in May. I am either going to keep the cactus on a screened in porch with a Southern exposure, or outside under a roof overhang during the rainy summer months that I will not be here. Any suggestions as to how large a pot I should plant the cactus in? Am I assuming correctly that it will be restricted in size if planted in a pot? If I snip a pad to plant in the ground, is there anything I need to do prior to planting it?