The Patent process itself, can be rather inexpensive for a private person.
The trick is to get the Patent in the door, with a provisional patent.
This allows you to market the device, to perhaps an OEM manufacturer, while being protected by the provisional patent.
That way, you can sell the patent, and let them finalize the process, or begin to license the patent, and pay the rest with those monies.
In reality, anything associated in aviation is a liability. Even though your innovation may not have been the cause, it will still be encumbered in the legal process, and you may be potentially dragged in.
That is why many of the patents are sold off to patent houses such as Intellectual Ventures.
Good luck.