Cap or Battery?

Ok, while I'm driving at night and i have the stereo cranked my head and tailights dim because I'm pulling so much power. The car im in is just temporary so everything thats going in it has to come out when i get a new car. So I've eliminated a new alternator. My budget is about $100, I could maybe swing $120. If I go with a battery it will most likely be an Optima Yellowtop because of the deep cycle, but i found a 2 Farad cap that costs less and ive never used a cap so i dont know how long they last... haha

I've got an Eclipse head unit, 2 Pioneer 2-ways and 2 Pioneer 3-ways, a Kenwood 920w/ 460w/RMS, thats powering 2 10" Solobaric Kicker L7s (600w/RMS each).

What should I do?

caps do nothing for SPL, they "might" help with dimming lights. The only real solution when the car is running is a bigger alternator, if the car is temp then maybe you should just learn to live with it for a while.

big 3

I do need to upgrade the big 3, I've just been avoiding it.

and besides wouldn't adding a second battery make it worse since itwould be adding another load to an already overloaded alt

I'm not talking about adding another battery i was just talking about upgrading my current battery

oh, those only help if you listen to it with your car off