The cost is astronomical to do something like that. You're better off replacing the component. Not the whole cabinet, just that one area.
Go on ebay and find a decent set of woofers. And if you want good, quality sound-- I recommend getting away from Pioneers. Cerwin-Vegas, BOSE and Infinity are ideal for home sound. Kenwood's are slightly tinny, but some folks dig them.
I'd also recommend staying away from dual voice coil. Too much power.