I think $24 is about as cheap as they come. Lowes is around the same. I think you are right about Walmart, never seen a case there.

OK, to answer my own question I went to all three stores today. Walmart only had one two pack of T8 4100K bulbs and wanted if I remember correctly $6.94 which made them the most expensive with the smallest selection. Lowes had a 12 pack of Sylvania 6500K bulbs for around $28.95 but I didn't buy them because the color rendition index was only 75. Home depot had a 10 pack of Phillips 6500K bulbs with a color rendition index of 85 for $24.97 which made the price per bulb about the same as Lowes but I bought the Phillips because of the higher CRI. It is rated 2800 lumens with a life of 36,000 hours. BTW, Lowes had some generic brand of 4100K T8s really cheap, a box of 30 for $29.99 which makes them only a dollar apiece. They were rated 2800 lumens with a cri of 75. But from what I read on this board 6500K is the best for plants so I bought the more expensive bulbs, and anyway I didn't need 30 bulbs. But if I had someone to split the box with me I might have bought the dollar bulbs.

Those Philips 6500K bulbs with a CRI of 85 will work great. $24.97 was a good price as they are usually $7 for a two pack. You need to keep them around 2" from the top of the plants. I built a pulley system to raise the fixtures which were suspended from sixteen inch chains that are used to raise the fixtures one inch at a time as the plants grow.
The pulley system raises the fixture several feet for working with the plants and watering.

Here is a link that might be useful: Mom's Garden

I was just doing a little searching and came across these Blue Max bulbs. They are expensive, about three times what you would pay for a bulb in a big box store, but they have 3300 lumens and a cri of 93 in a T8 bulb. Anyone ever try them and are they worth the price?
http://www.ultraluxlight.com/full_spectrum_fluorescent_bulbs_38_ctg.htm