My home DIY.

 

I would start with the Head Unit as it may be enough if your speakers are still good, I installed a Alpine CDE-HD149BT Single-Din Bluetooth Car Stereo with HD Radio, $225 from Amazon. I used the Modifry add on to control the radio from my dash. This was a big improvement over the stock radio as it produced higher sound levels.

Today I replaced my speakers with an Alpine S-S65C S-Series 6.5-inch Component 2-Way Speakers (pair), it comes with an adaptor mount that I used to mount over my stock speaker mount. You do need to cut some of the backing of the stock mounts as the magnets are much larger. Was not too difficult to modify as I just needed to drill extra holes that line up with the stock speaker holes, cost was $165 at amazon. The new speakers are way better than stock speakers, even though my stock speakers appear to look perfect. At 22 audio level my stock speakers sounds like garbage but now at 25 level with the new speakers is plenty loud on the highway.

I also picked up an KTP-445A - Alpine 4-Channel 45W RMS X 4 at 4-Ohms Amplifier, I am sure this is going to make things much loader but I think for most people it may not be needed.