its all going to be about your expectations. if you are looking for audiophile quality its gonna cost. If it was me and i was going to stick with the stock HU, i honestly wouldnt go crazy buying high end because your wasting money imo. get a decent set of door speaker components, that have a high sensitivity. throw them in the doors, put the tweet in the factory location. do some sound deadening. get a line out converter to a mono amp for the sub. you should be able to tap into the factory JBL, you should be able to tap into the factory wiring for the people with the JBL subwoffer to get your signals to your amp for your sub. If you do the work yourself you can keep the cost down pretty well. even going the dsp route has its limitations with the stock HU. they can be made to sound really good. i just wasnt willing to have a seperate volume adjustment to maintain my signal output quality. Like my lazy steering wheel functions
Im doing all ofmy work, and i am running a kenwood excelon HU, rockford power 4channel amp to focal ps165fx front speakers, and focal ps165f rear doors. did a good bit of sound deadening in front and rear doors. have a rockford punch 1500x1 amp and a alpine R 10" sub to be done at a later date. and im sitting around 2200. Of course if you pay to have it done, you can expect another 50-75% of material cost to be labor as well.