I actually just finished a pretty indepth bluetooth setup.
Definitely not a cheap way out to do it right.. My setup consists of this chain:
Bluetooth receiver -> EQ -> signal splits off the EQ into my tiny 8" powered sub under my seat and also to the F and R channels for the door speaker amp -> made a speaker harness off the amp to the new F&R speakers.
It's really nice because I got to keep my 90's Alpine in the deck for the aesthetic, but it has the modern sound and convenience. All volume and song control is from my phone. Connects automatically as soon as the ignition is switched on, just like any modern vehicle.