My husband lost his job on 7/23/09 and insurance ended 9/30/09. We did not receive any options for cobra until 11/28/09 and now are expected to pay back premiums which are very expensive. Can they legally do this after such a long period and after numerous requests by us?

Yes, he first should have known he had cobra rights and contacted them if you had wanted it ( or keep money saved back) But it is payable from the time the insurance ended.

Unless someone has health issues, you can find it though the private sector normally cheaper
But the price you are asked to pay is the same price the company was paying

They have 45 days from loss of coverage to notify you. It seems they have gone beyond what is allowed.
In any case premiums and coverage would be retroactive to 9/30. Depending on company size and/or state you reside you may be eligible for the 65% COBRA subsidy.