Wholesale Option/Exclusivity Contract ... With No Specified Price (At First)

[David Axelrod]

First post ever on BP. Go easy on me... 

Two existing owners of a duplex are willing to sell at the same time in an off-market transaction. It's a rundown old property on begging to be turned into townhomes, as is happening all across the neighborhood (and city). I'm trying to get the owner(s) under contract, and talking to lawyers for help with contracts, but want to make sure I get what I need... 

My question: Would it ever make sense to get the seller under contract with an option agreement that DOESN’T specify a sale price—simply a short-term exclusivity agreement to buy time to shop the deal to buyers? Sort of like an option to purchase the home at a price we haven't agreed upon yet.

Because this is a development play, and I'm not sure yet how much a developer would pay for the land after running it through feasibility, I don’t want to specify a price until I speak to those potential buyers… BUT I don’t want to get specific about the deal with those potential buyers until I have the seller under contract in some capacity. My idea was simply to get the seller under contract, promising to NOT sell the property to anyone else for 2 months. But if I did find a buyer, is it even possible to re-assign a contract that has no specified sale price on it? Would this method require a third contract, after a first exclusivity agreement (1), that listed the agreed upon price (2), before the contract was assigned to the developer (3)?

I feel like a need some kind of Pre-Option Agreement Agreement. Since my knowledge of the opportunity is my only leverage at this point, my main goal is to protect myself from getting undercut by a potential buyer who could try going directly to the seller—while simultaneously buying myself time to better gauge what developers would realistically pay for the land BEFORE offering the buyer any hard number. 

Do I just need to make the seller a "real" offer with a specific price? Or could I get him under an exclusive agreement with no specified price, then get him under another assignable contract at the price we eventually agree on? Am I overthinking this?

Thanks for your help. This would be my first wholesale play, and it's a great opportunity to get in the game, so I want to get it right.