Car Audio Geeks? New Car!

[rawfuls]

Okay, not really new, but new to me.
I'm switching cars with my mom so I can take her 2007 Honda Pilot LX to school with me because my old Kia Sportage isn't too unreliable, and I don't want to get stuck in middle of the desert and not know where everything is.

Anywho, I want to *lightly upgrade her audio, because driving in it and listening to the tunes is like listening to music from tin cans. Tinny, no bass, and just sounds horrible.

Budget of around $100-200 for the sub/amp, I'm sure I can figure out the speakers through crutchfield- but recommendations always wanted!

I definitely want to try and keep the stock head unit the same.
Like I said, it's my car temporarily, but my mother's overall, and there's no real point in upgrading it if when she gets it back she doesn't know how to use it.

I was thinking of upgrading the sub (I know the pilot has a super shallow port, but I'm so lost it's ridiculous), and installing an amp for that.

Speakers could use replacing, and I'm sure an amp is required for that.
For now, I want to focus on the sub/amp, and speakers can come when the money allows.

So my question- know of any shallow subs that will fit but also bump?
Amp suggestions/recommendations? I've never done an amp before, just a powered sub, so this one will be new to me.

I don't want to go with anything that will take up room in the cargo space, as it has a third row, and with that third row space is already limited as-is.

Thanks !

PS. I asked this question in the piloteers forum but they're not very..helpful