If I might suggest, inexpensive marine stereos exist aftermarket if you look... ebay, amazon, and buy.com...
Also, Shakespeare makes a VHF/FM splitter/sharer I just installed that works wonders for using 1 antenna for 2 devices. It forces a "switch" that turns off FM when you broadcast VHF. Seems to work pretty well.
Shakespeare VHF / Stereo Switch
I happened to find a radio that had no CD in it. Just used an SD card, or USB, with a single AUX port, of course with FM/AM. I think the whole setup, wire/speakers/radio/splitter worked out less than $100. It's not gonna wow an audiophile, but it'll crank out a decent amount of tunes.
Just make sure to put it on a fuse... DC is very easy to install. Red=+ Black=-/ground and life's good.