The torsion bar is the device that will prevent the suspension from bottoming out. Increasing the wheel rate is of major importance in a lowered car because you need increased resistance to compressingthe suspension with the reduced amount of wheel travel. The shock simply determines how quickly that bottoming occurs and will not prevent it from happening in all circumstances.
However, there are a number of decent shocks out there. If your looking for single or double adjustables there is QA1, Strange, Be Cool, Addco, Hotchkiss, Bilstein, Belltech, Rancho and more. Prices will range from around $125 to upwards of $400 depending on make, adjustment, range,and application.