Can you broadcast a very low power nav vor signal in air?
The use of radio transmitters is strictly controlled almost everywhere in the world. FCC would be the authority in charge if you are asking for the USA.

The International Telecommunications Union (ITU) is in charge of allocating frequency bands for different applications in the radio spectrum. You are only allowed to transmit if you have a frequency assignment, if your equipment is certified, and you are holding the required radio license.

There are use cases where non-certified equipment may be used (e.g. amateur aka HAM radio), or no license is required (e.g. wireless consumer devices like cell phones, remote controls, etc).

108.0 MHz is at the upper edge of the frequency band allocated to FM radio broadcasting, and the lower edge of civil aviation frequencies. Therefore 108.0 MHz is not available for experimental navigation signals. Your usage would be illegal. The same will be the case for any other frequency that can be used with certified navigation receivers.