I have the Scytek A10 for $30. It is a full alarm system and keyless entry. I also have the Scytek G20 for $45.
Scytek is one of the largest alarm manufacturers in the world behind Omega and Directed. They also make alarms for other brands. Scytek is not a cheap alarm like Bulldog, Prestige, Crimestopper, etc.
You can add whatever you want to AUX button. Some things will require extra modules like window up/down.