OK, I'm pricing the flash now. If I buy the flash, do i need to go with a fast aperature or will I be able to add more length?
That's sort of a loaded question. A lens with a wider aperture is almost always better than one with a smaller max aperture because it gives you the
option of using that wide aperture. Lenses with smaller max apertures are a compromise and the benefits are usually a lower price and a smaller, lighter lens.
When using flash, you typically light up your subject with the flash and the background is illuminated by the ambient light (unless you are in a small room, in which case the flash may light it all up). For many photographers, it's important to find a nice balance between the flash and ambient parts of the image...and in this case, it may be a great benefit to use a wider aperture.
If however, you are not critically worried about the ambient exposure and getting a perfect balance...then you will be fine with a lens that doesn't have an F2.8 aperture. You can shoot at F5.6 or F8 and let the flash do it's thing.
So, if you can afford an F2.8 lens, go for it, you won't regret it....however, a slower lens might have a longer range (the 17-85 or 28-135 or 24-105), which may be more of a benefit to you. It's up to you.
As for the price difference...who knows? The 2nd one is newer and probably in more demand because it's for digital...so maybe that's why it's more expensive.