I got a ES300 2002 and it has a 8 inch sub. The bass is not enough for me. I held a flashlight today to check how much the OEM sub moves and the poor thing works real hard and still cant do much. I'm not talking about the car-shaking booms, I'm just talking about regular music which you want to enjoy at a good volume with good clean solid bass. The ML subwoofer system doesnt satisfy me, as elaborate and expensive it is. And an 8" sub-woofer is too small. They should have had 12" (and made the removal easy too).

It looks like the best (an cheapest) way to go for me is to route a lineout from one of the rear door speakers, put it into a "line -> pre-amp" converter ($20), get an amp ($30, works fine), get a Hifonics 12" subwoofer ($40, great reviews), remove the old sub-woofer and disconnect the amp, use MDF to fit in the new 12" subwoofer (the hole is 7 inches across though but that should be fine). I had this cheap system in my previous car and the bass was great.
If I dont run into any big problems, this sounds like a good idea to me.

Any thoughts on this?

EDIT: I got it all set and installed after a lot of work spread out over different sessions. Basically, took out the car's sub, put in a 12" in a box to a nice amp, put in an REQ bass control unit to fix the bass too and it works good. Could be better but its good enough for me for now.