2002 impala

I own a 2002 chevrolet impala 3.4L and i need to know if getting a lowering kit for it would do anyting to my handling that would actually ruin the car . I need to get the kit because i am into car sterio and i am going to have alot of weight being in the trunk so i need to just level the car out so it dont sag no longer. I have seen that on www.pfyc.com has a coil over kit for the impala and it's $239.99 heres the link :

http://www.pfyc.com/store/merchant.mv?Screen=PROD&Store_Code=PFYC&Product_Code=IM4001&Product_Count=11&Category_Code=IMSUSP

If that will work please let me know, or if anyone else has a cheap kit please that would help to.

Hopfully sumone could help me out thanks ..