Cheap Audio upgrade from stock system

So I am the new owner of a 1999 PreRunner, which I love, but the sound just SUCKS!!! The system is just about completely stock (only thing that has been replaced is a new head unit, but judging by the looks of it- it's about 5 years old). Now I am a college student and don't exactly have a bunch of cash sitting around- but I am willing and ready to drop about 300 on some new equipment. I've done a bit of research on this forum and elsewhere- but most of what I found is from two or three years back and I'm sure things have changed by now.

My question is- What would be the best way to improve the sound in my car with about 300 dollars? What are the most important components? (Amp, Speakers, new Head unit?) Thanks!

 

Oh I left something out- I more than likely won't be streaming my music from anything but my Ipod (I don't own any CDs and I don't like the radio)- and my current head unit is equipped with a jack for it.

 

Okay! So i would buy new door speakers. Alpine is a good brand. I have alpine type s's

 

X2 I have alpine type-s in my doors, they are freaking awesome!

 

x3 on the Alpine Type-s

Definitely worth it!

 

What head unit is currently installed??