I buy my rub in 25lb sizes for $35. Try this website, they make rubs for many restaurants as well as Adkins brands which are sold at Krogers locally. One of the restaurants they do make rub for is Main Street BBQ in Euless.
They have a few different rubs that they market under the Adkins brand. I noticed that there are also a few products not listed here at the site. I will usually get the spicy bbq rub and split it down the middle adding turbino sugar for my pork and kosher salt for the beef. I then have about two gallons of each rub for less than $15 per gallon. Not bad $ wise. I have even sold pound bags of this rub at catering jobs I have done.
I do not use these for comps as much as I used to (I have used them on my ribs), but they do work well and I have done pretty well in comps using them.
They will also mix up custom blends!