Air bags would be the least expensive but you can't make it jump unless you use hydraulics. You can't pump the air fast enough to hop. Your psi drops with the first use and it takes a while to get your air pressure back. Hydraulics get their pressure from a pump. The bigger the pump the faster you can hop.
Maybe you could hinge the skid plate and hook up a power window motor to raise and lower it. Be sure to retract it when the cops pull you over and play dumb.
AL