yes, they cost usually around $500. What do you mean how much of an increase?? Lower your car to the stance YOU want it at, it doesn't really matter. Yes, your stockies will last a year tops depending on how rough you are on your car ie hitting potholes and bumps and such. Reason being is that the stock shocks aren't made to handle all of that excessive pressure put on them and end up blowing out resulting in a really shitty ride. As for websites umm....
www.modacar.com www.lightningmotorsports.com these are the two I use most of the time.
Also, I believe in the saying "Do it once and do it right" I think you'll be very disappointed with those low quality springs....it's better to save up and do it right with good quality parts.