I want to lower my hhr as much as possible without anything getting damaged, including when i hit a large dip on the freeway

Realistically, i would be happy with the top of the tires being aligned with the top of the fender (or bottom, depending how you look at it)

What would be the cheapest way to do this?

 

There are many brand of springs that will drop you about an inch or so. But to get as low as you want will require coilovers. Not cheap, and would likely bottom out on speed bumps. Looks killer though!

 

Eibach sportlines will prob get you the look you're after. $2-250 + alignment for sure with that drop.

 

I went with Progressive in Anaheim 2 in. in front 2 1/2 in the rear but thery stopped makeing them but would if enough reuests, Eibach used my HHRto redesign new springs, 1 person recently got them said the rear dropped 2 1/4 inches, Eibach could not tell me how much their springs would drop the HHR.

 

H&R or B&G springs are a bit lower than sportlines going by the pics.