Here are some affordable coilover options with spring rates at or near 400lbs/in:
http://www.ft86speedfactory.com/rs-r...l#.WHQdAlPyuUk
http://www.ft86speedfactory.com/rce-...l#.WHQdBlPyuUk
http://www.ft86speedfactory.com/rce-...l#.WHQdEFPyuUk
http://www.ft86speedfactory.com/mega...l#.WHQdNFPyuUk
http://www.ft86speedfactory.com/kspo...l#.WHQdSVPyuUk
Of these, the RCE T2 is the only one that is delivered as a true DA right off the shelf. IMO it's the best bang for the buck if you just want to plug and play. You need to bring your own top hats to the game but you can reuse the stock rears and find some cheap front plates to get your front camber. My toughest local STX competition has spent roughly double what I have on shocks and isn't faster than me, so you can definitely take the fight to the pimp shock crowd with these.
I thought I saw a KSport that was a true DA somewhere but couldn't find the link. The Megans can be converted to true DA as well for extra $$$. Off the shelf these will have a single knob that adjusts rebound and compression together, which is less than ideal but you can make it work decently enough. The T0 has no adjustment but is still a decent shock.
Come to STX, the water's nice.