sparkys are about 72.00 from dune land. there is a 94 db limit, and of course you have to have a flag (duh) I would say as long as its an off weekend you will not have any problems. I always take my bike in, in the back of a truck so they don't hit me for db, remember the sparkys will make your bike louder, I slip them on till I get in, then I take them off and leave them in the truck, never got a ticket yet, just remember if you leave the dune area and try and ride back in without them you will not get back in!! if you can't meet db, stick some steel wool in the sparky between the silencer and the sparky till tyou get in and it will make it meet db.
but like I said earlier, if its and off weekend you will not have any problems, they get real strick on the big holidays.