The actuator isn't working. You should be able to manually move it, assuming you can see it from the passenger side, under the dash. The cause can be mechanical binding or something is jammed in there to prevent it from moving. The other possibility is that the selector control isn't working. Sometimes, disconnecting then reconnecting it will solve the problem. You should be able to find instructions to disassemble this on the internet.
I'd say it's very unsafe to drive. Breaking a leaf spring isn't easy. It had to have taken a substantial impact. In the worse case, you may have even bent the axle. The cost will vary a lot. If you can do the work, get a used leaf spring from the junk yard. If not, a repair shop would probably charge you a couple of hours labor plus parts. You should be to find specific cost information for the part on the Internet. There are labor guides too. Then you'll know if you're getting a fair price for the work. You don't have to go to the dealer to have this fixed.
A couple of things come to mind. Start with the simple stuff. Look for small rocks anywhere on the bike, assuming you can't localize the sound. You an pick them up anytime you ride and the will lodge themselves into interesting places. They seem to rattle at specific RPM ranges. Loose accessories will do this too. The more technical possibility is a defective catalytic converter. The catalyst separates within the converter causing a loud noise. It sounds a lot different than the sound you hear when the bike exhaust cools down. This is more of a possibility if you have an aftermarket exhaust. This should be easy to confirm. Once they take off the exhaust, just shaking it will move the catalyst around confirming your problem.
I don't have any specific experience with this problem but you can try these: Remove the alarm fuse. You should be able to look at the owners manual to locate the specific fuse, if there is one. Disconnect the car horn (assuming this is the source of the sound). This won't stop the alarm from activating but will silence it. This solution can drain the battery too. Disconnect the battery while the car is parked.