There was always a full retail price because you could purchase the phone without an upgrade. Just because it wasn't unlocked didn't mean you couldn't buy it full cost without signing a contract. It was called the "no commitment" pricing.
iPhone 3GS
https://forums.macrumors.com/threads/717252/
iPhone 4:
https://community.verizonwireless.com/thread/601170?forceNoRedirect=true
After doing more research it turns out that for AT&T, the retail price went up to 649/749 with the introduction of the iPhone 4S. But like stated above, with he introduction of the Verizon iPhone 4, retail price went up for the iPhone 4, but that was strictly Verizon. So in a way we are both correct.