Maybe I missed it, but I gotta ask. If the tow company dropped your bike, why is YOUR insurance company paying for the damage? The insurance company has insurance for just that kind of thing and they should repair your bike to the way it was before their guy(girl) dropped it. If they want to give you a hard time or refuse to pay, simply file the small claims court paperwork. It is pretty cheap, fast, and most-likely you will come out with an order for them to pay you what you are owed.
If for some reason your insurance company feels compelled to take on the costs of the repair, they should appraise the cost of the repair and either cut you a check or have it sent to a shop and fixed with new replacement parts. You should not have to be trolling Flea-Bay looking for a deal to fix something that was not your screw-up. It really sounds like you are being screwed around.