350-450 a set for king spring?!? Jst the springs???
Mate, if that what you paid you got ripped off by heaps!!!
For my VXII S i picked up all four, SL front and SSSL rear for 260 bux!
Also if you go any lower than SL and even with SL your looking at a camber kit.
UNLESS, you have a heavy duty tow bar installed as they normally come with a camber kit already.
I'm not sure about the installation cost of a camber kit but my mate just picked one up for 140 bux i think.
And finally the sorten shocks and struts...
Not all THAT essential but you will have a fair better ride with them.
Also, you said that you want it as low as you can, if you get i think SSL and SSSL in the rear you rear spring will not be captured (Shortened shocks fix this) and your mechanic will tell you off for it as each time we cuts your car up on a hoist their fall out....
Final note.
The commodore rear suspension assembly is offset to the left by about 10mm,
buggered if i know why but thats how it is.
Is you lower it to SSSL you will have to make sure that your current rims or future rims have an offset on them that doesn't caus problems.
I know when i got my 19's first tucked under my baby the rear left rubbed on the lip inside the guard so i had to get that rolled (50 bux for a job that if done properly the paint will be fine and uncracked or alot more for getting it done by someone who doesn't have a clue and cracks you paint and having to respray)
Hope that answers your question