[BIGglaSS]

I think you can accomplish your goals within your budget. Every year there is new technology coming out, it only gets better.

You can keep the original radio as a dummy, and use bluetooth to stream to a hidden system. With some fabrication, you may be able to install a master volume knob in your original AM radio to control the system.

To have full, complete sound, you still need a decent subwoofer. You're not using it for the boooom boooom, but it is still needed to compliment full range sound.

There's several ways to skin this cat. For entry level, I would chose a BT streaming amp, 8" subwoofer, and a component set for the fronts. No rear speakers needed. You can easily do this within budget.

Are you planning on kick panel speakers? Or, Door mount? Or utilizing the dash speaker?

I estimate $3-500 on amp, $100-150 for sub and box, $150-250 for component speakers, $25 -100 wiring/install supplies. If you want tuning capabilities, you need a DSP (digital signal processor), add another $150 entry level or $800 for top of the line.

Need a little more info on where you want to mount speakers, and whether you want tuning capabilities or future mods before I could recommend what amp setup. But for components, look at JL Audio, JBL, Morel, Focal, Image Dynamics. All can be had for under $250. For subwoofer, Image Dynamics ID8 or JL audio 8w3 will get the job done in a small enclosure.