Each of the stock 10" woofers has an internal amp, the only way to fix your current problem without going completely aftermarket is to just replace the blown speaker with another from GM. You can probably find a takeoff for pretty cheap.
If you are willing to remove the stock woofer setup and add a sub in the trunk, the aftermarket possibilities are endless
The simplest and best "bang for your buck" solution would be a 4 channel amp, ch 1 + 2 going to front components (6.5" on custom plates is popular), ch 3 + 4 bridged to the sub.
I put in a 5 channel amp (with dedicated sub output) since I like the rear speakers being there. My specifics are in my sig.
The first thing you need to do is decide how much $$$ you want to spend. A simple amp/sub setup that sounds great can cost under $500, or you can go nuts and spend thousands. Check out the 'what do you run' sticky thread to see if anything jumps out at you.