On a different tack, what about aircraft VHF?
Whilst continuous transmission on an in-use frequency would clearly be unacceptable, if there is an airfield in your vicinity with separate tower, approach and ground frequencies - can you negotiate temporary "loan" of the frequency for a few hours at a time when it wouldn't be in use? (E.g. the ground frequency at a time when the airfield happens to be closed to traffic and is only using the approach frequency?)
G