All you would need to replace is the OEM struts. Everything else can remain the same (unless needed to be replaced for maintenance purposes.)
The only issue is if you are going 3 inches, that is pretty low for the vehicle. The subframe, oil pan, side skirts, and some other components might scrape if you are looking to daily the vehicle with that height.
I am lowered 2.5" and I can no longer put a floor jack under my vehicle at any point, whatsoever.
You could get some pretty cheap coilovers for maybe $300 brand new, but I would not recommend that route. The best investment would be some lowering springs paired to the OEM shocks, as that would provide the best comfort-per-dollar on a daily driven vehicle. Just my 2 cents. I wouldn't want to drive a car that gives me tremors after getting out of it.