Lowest cost would be an on/off pneumatic switch operated by a servo. Many people have had this setup work perfect for a very long time. The mini hobbies is around $89.00 there are other alternatives in that price range. I hear the trim setup works but I've never used it. I have one new in the package never used. I'll sell it to you for $40.00 shipped as I'll never use it, but it will get you going. Contact me offline if you're interested.