I need help finding a site with low rates on bus tickets!?

ok so i like in Greenville South Carolina and i need a bus ticket to Norman Oklahoma. i need help i cant find a site that will give me a rate on how much this will cost and were the bus will be stopping ya know all the basic stuff.... i am limited to money but i REALLY need to go! so please if you know of any sites that could help me that would be wonderful! and like i said please only tell me about the site if the tickets are cheap. i am VERY limited on money!