Hi... Picture this, if you will. I wish to take a picture of my High
School class reunion, and, be in the picture also. I set up my 35 mm.
camera on a tripod, set it up to take the picture, but the time delay
will not allow me enough leeway to get back into the group.
I have found a low voltage selonoid, that I hope to be able to modify
to 'push' momentarily, a camera shutter release cable. But I need to
find a keychain type transmitter, and battery operated receiver, to
function the solenoid. I see car remote starters being installed all
the time, and car lock releases, all of which are dc Tx, and, Rx units.
But where can I find a cheap single channel system?

Yes you do see them all the time but they are made for such a huge
market the cost is minimal,to actualy buy one off the shelf capable of
doing what you want would be expensive and hard to find.
Two options are to canibalise a unit from something else and use that
or build a tx/rx pair yourself from descreet components.