any lowering springs on stock absorbers will result in a junk ride quality. get adjustables. tein ss is good, but will cost you more. for your budget, go for bc racing. gab ss is similar (produced from the same bc racing factory), but get the original la since the price is not much diff. to use adjustable effectively, you need to find a good installer. setting up is very important to get a perfect ride.
if you are concerned about stiffness, get lower spring rates. know the stock springs rates of your car, and get something like 2x stiffer springs compared to the stock spring rate. the spring rates of bc racing for inspira is 8k fronts and 6k rears. that's plenty stiff for road use.