A provisional patent is what you're looking for. It's cheap and easy to file, and gives you protection for up to a year, during which time you can have peace of mind as you disclose the idea to developers and get the ball rolling. Good luck!
From IPWatchdog:
Why provisional patent applications a good idea
One reason I like to suggest starting with a provisional patent application as a way to initiate the patent process is because they are cheaper to prepare (because there are no formal requirements) and the filing fee due to the United States Patent Office at the time of filing is only $130 for small entities (i.e., individuals, universities and companies with 500 or fewer employees), which saves you several hundreds of dollars compared to the filing fees for a non-provisional patent application. Indeed, the filing fee is even less — just $65 — if you qualify as a small entity. See USPTO Implements Micro Entity Discount. Regardless of the filing fee to be paid to the USPTO, provisional patent applications cost less to prepare from an attorney fee perspective because there are no formal requirements, which means we can focus on disclosing the invention in its full detail while still preparing an exceptionally detailed application that costs only a fraction of the cost of a nonprovisional patent application (i.e., regular patent application).
Assuming you have filed an appropriate provisional patent application you can market the invention without fear of losing patent rights, generating cash to proceed with development or further patent activities. In other words, the provisional patent application is an interim step along the road to a patent.