Serious Purchasing Confusion

I recently attempted to get a new phone w/ AT&T I was told I would have to make a $500 diposit but the man was nice enough to reduce it to 100 still unsure if my contract was gonna go up I refused. I decided I wanted to get an iPhone. I attemted to purchase one through AT&T's Premeir store so I could obtain a student discount on my plan. I was denied and told they could not sell me the phone at all and I qualifed for a prepaid plan. I attempted agian through the regular AT&T's site and had the same message pop up. BUT when I logged on to the Apple Store's website I was told that I would have to make a $150 diposit at an apple store or AT&T store. My fear is that upon arrival the sales rep will back track and say that my diposit will be higher regardless of what the site said. Anyone have any input?