Actually they now have aftermarket command start where you use the lock button on your GM FOB. You press lock twice then hold. This way you don't need an extra FOB. Or you could get the remote start dealer option, may or may not be more money depending on dealer.
I usually stay away from electrical additions because most demand some kind of rewiring work.
Aside from that, there are affordable options out there for less than $200, installation is probably where the cost goes up.