On the 100cc, you could use 2xHS985's on the rudder or one or two 7955's.
My preference would be a single 7955 or the new 7980TH on each tail surface. It's way less complicated than a dual servo setups.
Don't see how cheap you can do a 100cc. It's a different game.
7985's might be OK on the rons.

Do yourself a favor and use unregulated a123's for power for the servos.