Recommendations for speakers and sub

[BttleFedC10]

So Ive got a 2015 Ecoboost Mustang and the speaker in it aren't really that great. Needs an upgrade. Now i don't need anything overpowering. Just want something a lil better than stock. Don't want it rattling things around in my car.

[EW]

There are many 5x7 coaxial speakers that will sound better that stock. JL Audio, Focal, Alpine, etc all make inexpensive and expensive options starting around $99pr.
A single 10" woofer is as small as I would use. Alpine amp, enclosure, Alpine woofer, wire, labor, $544 installed +tax. Optional sub volume knob $35. More power and better sub(s) will sound better and cost more.

[GT Fanatic]

Having the right tuned box will make a world of difference in sound.