If you're planning on selling PHP code you're dreaming.
mikeatrpi is on the right track. People are not going to buy your code... but, people will pay for a fully integrated system. You're either going to have to integrate your system into their systems, or host a system to make any money.
I think that's the main thing people don't understand about open source. If you make your code open source all you're doing is allowing another programmers to see and possibly use your code. People that are going to spend money for what you've developed are not interested in your code, they're interested in a system that will solve for whatever problem they are faced with. They also want you to integrate/host, and support it as well. That's where your code obtains value. The code itself is not going to make you money.
There's a paradigm in the development world that says you can make money from simply programming. Unless you're programming for a company you're not going to make money by simply writing code. Back in the day this may have been true, but times have changed and are continually evolving. You're going to have to change the way you think about development if you want to keep up.
What kind of systems have you developed that you're trying to sell anyway?
$50,000 for a degree?! Good hell, what university did you go to?