Upgrading to JBL sound system on 2004?

I recently bought a 2004 Prius and so far, love it. It has the standard stereo system with cd player, which in my opinion sounds great- but... I play music from my phone quite often, and using an fm transmitter just doesn't cut it. I used to use a cassette adapter in previous vehicles, but my Prius doesn't have a cassette player. Nor does it have and aux input. I'd like to upgrade to the Jbl sound system (if po$$ible) and from what I understand, that would give me the aux. input I'm looking for, along with better sound. Am I totally out of line for thinking it's even possible? Any other options that I may have that would still allow the steering wheel controls to function? Not looking to spend an arm and a leg, but want it to work properly... All opinions welcome and appreciated!

 

I actually think the stock system (basic Toyota cd/am/fm with 6 speakers) sounds great... Many times better than the one in my previous dodge caravan! The stereo system in that car was flat awful.. The rear door speakers would rattle and distort at any volume louder than a normal conversation! My only issue with the prius' sound system is that I have no way music from my phone, and that's very annoying. Doubt I'd upgrade speakers. I don't like big loud thumping bass, and I don't run it at max volume, usually somewhere between 15 and 40. How involved and expensive would it be to replace the stereo itself? I would imagine I could get my Dad to do anything that might require soldering, and I could probably do the rest. All I'm really looking for is am/fm/cd and aux input, possibly bluetooth but not a major requirement. Doesn't really even have to be a touch screen.