You need to buy some lowering springs: H&R sports 1.4 inch lowering; Eibach ProKit 1.2 inch lowering; Voltgand or others (?). Do a general search of the forum and you will find what members have used.
You also need to change your shocks to a set that will be valved to deal with the lowered springs. Generally, members use Bilstein Sports or other more expensive and exotic shocks. Penske & Koni adjustables come to mind.
Luke at TireRack.com has most of this stuff and you are looking at about $250 to $300 for lowering Springs (maybe less if you shop on ebay) and about $400 or more for shocks (depending on what you get).
Installation costs will depend upon your shop's hourly rate or your abilities. Generally, replacing the shocks and springs together should take about 3 hours (more or less depending upon the shops skill and unforeseen complications encountered, eg. rusted on stuck bolts, stripped threads, etc). On the east coast I have paid between $250 and $500 total for installation of both items. Others on the forum have had this job done for a lot less. It is not that complicated, but to do the job well you will need a proper spring compressor, preferably a hydralic lift and various wrenchs, sockets and lubricants -- sometimes a torch is needed and an air powered socket driver is a great thing to have.
Good luck!