Programmatically Go Through Several .aspx's Business Logic?

I have several successive web pages going through a checkout process and they each have tons of business logic that time restraints limit me from pulling out and wrapping up elsewhere in the code the way it needs to be. What would be a good method for calling each one of these pages' Submit buttons in order from one page to the next?

The way I was going to do this was to (laugh at me go ahead) make PUBLIC all of the submit buttons' code and just call them. But what I have found is that all of them have, of course, certain calls to controls on their pages where it might make a label visible or change a text property then that will crash the app due to a null reference. I believe it is basically saying if the webpage is not visible then it is not going to let the code start setting certain GUI properties of the controls on the page. It seems like I recall this in VB6, too.

Anyway, what would you do if you were in this situation? I have started down the path of creating a flag that says whether or not I am in expresscheckoutmode and, if so, it just doesn't do the "illegal" things mixed into all of the code like making labels visible and all that. But that also means that I have an IF BLOCK everywhere where the code simply changes a label. It junked up the code bad and I still haven't finished that implementation of it all. I wanted to come here to ask the collective mind what programming principles I can best apply here.