Ideas for a new low budget stereo in a 01' wakesetter

So i want to get a new system in my 01 wakesetter. Everything I have now is either stock or very s***ty quality. Right now i have the stock infinity speakers, pretty happy with them actually, for inboats. I know there are much better speakers out there but dont really have the money. I have also 4 s***ty speakers in 2 cans on the tower and they stink. I would like to switch up the tower speakers with something decent and add a sub. The inboats and tower speakers are run off of a 4 channel amp right now. Pheonix Gold i believe. I also only have one battery and its in the rear locker. Probably would be in my best interest to add another and maybe change location. IDK how hard that is but hopefully not a huge pain. Hopefully David from earmark chimes in on this because I think he is like the stereo Guru on here and WW it seems. Maybe you guys could come up with a mock system for me and throw around a price range of what it would be! That would be sick.