Somebuddy has got to make a "Subway,Mr.Sub ... :lol: " sponcered audio ride.
pffffff, 3 12"s is the bare minimum. actually if you find one sweet 8" you'd be happy. something along the lines of an 8"RE sub. hard to find though.
I've got a single 10" Infinity in a sealed box in my focus, it sounds very nice. It actually only cost me around $110 for the sub, the box and a 200 watt amp. I'm sure you can get the same sort of deal if you look around ebay for a bit.
I have 2 10s... may be more than I need, but I like em :)
I upgraded the 12" Pioneer IMPP to a 12" Alpine Type R and huge difference. This thing sounds awsome in the Focus hatch. Its all you need..
I started with 2x12" alpine type-s in a sealed box. I recently had 1x12" adire brahma in a ported box... loved it, sold the car. Now the brahma is going in my sonoma in a sealed box.