Some times ago, a Pro Writer (let's call her PW) called me to discuss her situation. PW created a show for a producer a few years ago. The contract agreed that this producer (who contributed some ideas, but maybe didn't do the heavy lifting) would be a "co-creator." Nothing has happened with the show lately. What can PW do?
Legally, PW can't do anything without the original producer's okay. He has co-ownership of the copyright from the ideas he may have contributed.
In order for PW to take the show out and sell it, she needs to make a deal with OP. You can't sell a show that someone else owns or controls. So PW has to get OP to agree to take a step back.
What's a fair deal to offer?
Whether or now PW did the heavy lifting is irrelevant because the deal was a co-creating deal, and the producer did contribute ideas. He probably won't take less than shared Created By credit of the TV show. He'll want a share of the Purchase Price and any royalty. He'll want an appropriate courtesy producer credit -- maybe Co-Producer, or Co-Exec Producer, or (you want to avoid this) a guaranteed Exec Producer credit.
The same deal works for movies. When you see Bigname Director taking an Executive Producer position on a movie he didn't direct, odds are good that he was on the movie as the director during development, and the studio bought him out for some reason or another for money and a courtesy credit.
PW should have OP sign an agreement
that puts control of the show in PW's hand, and acknowledges that he doesn't have any right to share in PW's further
involvement in the series. So PW would be free to negotiate her own status on the show if goes: showrunner or Head Writer or whatever she can get. She would get paid for any scripts she'd write. Her salary on the show would not be shared. (Remember, "an oral agreement isn't worth the paper it's written on.")
Likewise in the movies, PW would have to share the purchase price of the original script, and the credit accorded the original script, but not anything she'd get paid for a later rewrite.
That's a reasonable deal for everyone. There is still plenty of money in the deal for PW, and enough for OP that he has an incentive to let it go get made elsewhere.
If you can't afford a lawyer to draft the agreement, then write something up in a couple of pages that spells everything out. You'll eventually have to sign something written by lawyers, but most people, having agreed on the substantive points, won't be too much of a dick about the legalese. Just be aware that when it comes to the Big Legal Agreement, any ambiguities you've left in the document will probably be negotiated in favor of the party that has the least to lose.
This is why you want to be clear what rights you're giving up. You might be focused on the up front payment now, figuring what's the odds it will actually go? And I really need to fix my bike. But eventually something does go, and you might be kicking yourself later for a too-generous deal you made long ago.
On the other hand, don't be too proud. If I originated the project, or even if a producer brings me in to adapt something from another medium (e.g. producer has optioned a book), I am unlikely to share my created-by credit. But if it's the producer's idea, then I might co-create with him. I'd just evaluate the rest of the deal. I recently wrote up a pitch based on a producer's concept. I share co-created by credit. I agreed to come on board because his concept was good; it was easy to see how to develop it into a show. I got paid appropriately to do it. It was a short time commitment. The producer is a heavy hitter with good credits. He can get something made. I had the time. Why not do it and put another iron in the fire? I'm not proud about sharing credit when there's an argument for it.
With a less heavy producer, I might have been less interested in doing a co-create. Or with a producer who likes to keep picking things apart and rethinking them. Or if it wasn't obvious how to turn the concept into a show. You have to consider all the factors. And then, of course, get everything on paper.