I've looked at the keyfob/remote refurb kits on ebay and it seems a bit steep at near £20 for a plastic case and a battery? anyone seen cheaper?

 

I believe you should be able to find it for a bit less. This is part of the receipt for the auction I purchased from a while back(9/24/10). Unfortunately, it doesn't look like the seller has any on eBay at this time.

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Seller User ID: carkeysolution

Your total is:
$7.99 per item
insurance
$0.00 Sales discounts (-) or charges (+)
$0.00 shipping/handling

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$7.99 = Total
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no where near as cheap as that even in dollars! Hong kong sell one much cheaper but its the wrong sort!