I'm looking to get the actual AC adapter, in part because I like having the original components to a system, and also because I know it'll be the proper voltage and amperage as opposed to a 3rd party product. I've been using a Genesis AC adapter for a while now without issue (it's a 9v supply vs a 10.5v supply, but it works all the same), but should I ever decide to sell it, I'll have the official AC adapter to go along with it.
So I'm guessing that, while probably on the high side, the prices I've seen on eBay aren't too far from the truth in cost, are they?