Well done with the Bonhams buy, Chris. I hope it comes together smoothly.
Re the high price of the ebay bike: Sellers are free to ask what they wish, just a buyers are free to decline to purchase. Some bikes, like the 2 3/4 Douglas, are sufficiently common that another will be available at some time in the future, perhaps a better example at a lower price, perhaps not. This, at least, gives us a chance to haggle with the knowledge that it won't be the last chance to buy the bike of our dreams.
Yet if you were rich (count me out!) and did pay too much, at least the bike is running so you can get fun out of it without the struggles of restoration.