This would be an interesting conversation to watch (and pretty loud too I suspect) if we were all in a bar drinking beer together. (Slurp!)
Seems like there are basically 2 sides to the answer...
- Be selfish, sideline the pro and charge $$ (LOW ROAD)
- Be ethical, support the pro and charge 0 (HIGH ROAD)
In both scenarios, the OP still walks away with the same wedding experience gained on the day. How much more does he expect to gain? The answer to that question really comes down to his ethics, scruples and conscience. I know what I would do and it's clear what many on this forum would do.
If it were me, I would be honored, extremely humble and appreciative if any professional of any craft were willing to jeopardize their livelihood by having my inept and inexperienced greenhorn ass in their way while they are trying to make a living. If I turned out to be an asset, wonderful for everyone. But the risk that I slow things down or disrupt the rhythm is high and so I don't expect compensation. I just want to learn and I would be grateful for that chance. Pay me later when I deserve it and that is up to the pro who is putting up with my sorry ass.