The wet/dry is fairly easy to use. Water from the tank will go through one of the bulk heads, go into a driptray with filter floss and Chemical media of you choice, drip down through holes in the drip tray into the bioballs. Then the water will go down throught an eggcrate and back into a poly type sponge. Then the water is in your sump area where you will house your return pump(a Mag 2, my suggestion). The water will then be sent back up tubing and through a return elbow and back in to the tank.
As for the changing of the media and bioballs. Never change the bio balls. Clean the filter floss and poly sponge every 1-2 weeks according to how dirty it is. Change the chemical media as per the instructions on whatever type you decide on.
I only have one wet/dry that has been used on a bunch of different tanks. It cost me $80 used. I'm not sure how much a new one would cost. Look at
http://www.wetdryfilter.com.
