In 2014 we sold 27 gsm controlled relay remote starts installs. The basic unit is $199 for the remote start and an extra$250 for the ability to start from cell.. Can a wrong number start your car? Yes but if you unlock the doors, hit the brake, rev the engine, open hood or put in gear will shut the engine off, also the system only runs for 5-10-15min programable then shuts down anyway, so a wrong number Is not a big deal. Its no different than setting on the RF key fob that also can start the car. Rf even long range units usually cant start your car from inside the mall when its the middle of winter here in Michigan. So yes a cheaper solution here is a prepaid cell phone as a trigger for the remote starts we already install the systems anyway. If I can offer a unit for $99-$159 many more of our customers would add the feature. Also if the customer is worried about the wrong number problem we can simply program the remote start to lock doors when the car starts this feature is on all units we install, then set the phone to a standard ring tone with no vibration low volume and then turn on distinctive ring tone and set it to vibrate on what ever number you would call from standard features on most phones.. AS far as "strange strange requests with no explanation of the end application" I put exactly what My needs were in the original post..
Again thanks for helping.