Hi John
I'm doing the same exercise for my HEQ5.
I've found this one from the UK for $41.17 ...
http://www.ebay.com.au/itm/Celestron...item415b94156a
and this one from Hong Kong for $3.08 ...
http://www.ebay.com.au/itm/12V-24V-C...item487e265abc
I am not at all knowledgeable about things electrical but gee, they look like they do the same thing assuming the plugs are the same. I would imagine you would have to fit an inline fuse with the cheaper job.