What is the cheapest remote start module?

Newbie here.  Have a question concerning a potential christmas gift.  I want to get someone a remote start system that will be compatible with a factory keyless entry system.  I have seen stand alone modules that will activate off the factory keyless entry if you hit the lock button twice.  I don't want to have 2 seperate remotes and I know this person likes their factory keyless system very much and wants to keep it.  So, what brands and approx price + where does one look to get one of these systems?  This will be going in a 95 Chevy Beretta with factory keyless entry.  Thanks for the info in advance.