Josh, by the time you replace the speakers with something decent your pretty much gunna double or tripple the cost of building one on your own.
So far (I'm piecing everything together before i start) I'm at a whopping total of 120 bucks with shipping for building my fiberglass headliner, and I got way more glass then I need.
So far I have a set of kenwood components oversized 6 1/2", 40 bucks new in box from eBay, 30 feet of 50" 7oz strand mat 50 plus 10 shipping from eBay, and I should only need about 10 feet of it. Some pre made flush mount mdf rings for 15 shipped ( cause I lack a router and wanted them perfect), and some fabric from Jo Ann's that was a remnant for 5 bucks.
All I need is resin, at most a gallon, and that will cost me 60 shipped from us composites.
So I'm at a total of 200, and depending on what you value your tinker time at you will come in way less then what that headliner will cost. Plus it gives you a lot of custom ideas, I plan on glassing in my exp ohc, and if I can find one I like a cab light that is a step up from my current setup. And you can cover it how ever you please on headliner material or do the body work and paint it. Just some food for thought.
Better speakers then you could add in anyway, cheaper, a high level of customization as well as a pride of doing something awesome