Any good branded pre which has 2 pairs of rca's. The easiest buy is the apine headunit that came with the city and facelift 10th gen corolla's. Those should cost you around 5-5.5k.
You can either go for 6" or 6.5" coaxials at the front ( components would be better but I'm suggesting a setup where you won't need an amp and all the wiring hassle) or 6x9s at the back ( for which you might need to make a rear board). Most 6x9s like to be fed power from an amp at high volumes so if the coure has front speaker mounts, stick to front coaxials. Front coaxials (good ones too) will cost 5-6k.
Finally, get a pre-amped subwoofer. Pioneer has a 6" subwoofer that comes with an inbuilt amp and a remote wire. All you do it is put it under the seat or trunk ( it's small so fits almost anywhere), power it from the pre and place the remote with you. You can power the sub, increase the bass output and changed the phase output of the sub from the remote.