The torsion bar is a piece of piss, and fitting springs is an afternoon job. You could have your car lowered in a day, just give yourself time, get a mate to help you and buy some tools. Find the guide on the website and have a go at it yourself, if it goes wrong (which it prolly wont cus its easy to do), then you can take it to a garage and get ripped off there.
I was asking for prices on getting my 1991 RT lowered as I was dead scared to do it myself and c0ck it up but since I lowered mine, Ive lowered my mates RT and hes lowered a new-ish shape Rover which is a springs all round jobbie.