UPDATE:

Of the many forms I submitted for a repair estimates for the lens only three companies have responded so far and they are CameraSolutions in Portland, OR., Advance Camera Repair in Joliet, IL. and Perfect Image in Lancaster, PA. SO far even Sigma, has not responded to a request for repair estimate.

The last two outfits did a very thorough job of filling you in.
Of the three that responded - Advance Camera Repair in Joliet, IL said "We would be happy to take a look at your camera. We will have to see it to confirm the problems and give you the proper estimate. We provide a free estimate in 1 day . The repair time normally is 7 days."

Camera Solutions in Portland said "Thanks for reaching out! That is a common issue with these lenses after a certain point. If I remember correctly, its probably the aperture unit, or a bad flex cable in the lens. 

Feel free to drop by the store when you have some time to drop it off. We take a $24 deposit and our turn around for repair is about 2-3 weeks. I can ask a technician for a rough estimate when you get here. They are not in at the time of me responding to you. After, we will take it apart, diagnose, send you an estimate and you can say yes or no from there. "

and Perfect Image said - "Thanks for contacting us! It sounds like the aperture unit in the lens has either failed, or the electronics controlling it have. We cannot get the service tools required to properly work on that lens, so we would have to send it to Sigma for service. It would most likely cost between $200 and $450 to repair. Sigma would provide a more accurate estimate before starting any repairs. If you have any questions feel free to reply to this message. Thanks again and have a great day!"

All gave me a name and phone number to contact them should/if I had questions.

The closest place to have it repaired is in Portland which is a 200 mile round trip. The others would all have to have the lens packed and shipped.