350-750$??? Damn that's Cheap!! Most coilovers I see are in the 2000$ Range!
Luca..You aren't recomending just the Sleeves are you?? Those are Garbage! If your gonna go adjustable, you gotta get the real deal! Or else just get springs!
I was recommending just the sleeves if price was a problem and you don't care how your car rides. If Handling is a concern then definitely go for the full coil-over kit, but get ready to spend big bucks.