I don't vend or make large amounts of rub but I still make my own. I imagine you could save a lot by doing the same. Paprika, Kosher Salt, Black Pepper, Cayenne Pepper, Chilli Powder, Onion Powder, Garlic Powder, Turbinado or Brown Sugar and some other special ingredients like Celery Seed, Cumin, Coriander, etc... will get you a decent rub for a lot less... YMMV...
I've purchased some items from this place and was pleased with the price & quality.
http://www.sfherb.com/ I'm sure there are better places... Cheers!!!