Accounts for special orders

[Admin]

I've not been able to find an answer in the archives on this, so I'm
hoping someone here can point me in the right direction.

The topic is "special orders".  I have a small business.  Customer Alice
wants me to order a SuperWidget.  The price is to be $500, and she's
given me $250 earnest money. 

Vendor Bob is currently out of SuperWidgets, but has them on backorder. 
Current cost is $400; I will not be billed until the item ships.  Should
Bob be unable to obtain a SuperWidget for me, then the whole deal is off
and Alice will receive a full refund.

So . . . how to enter all these.  I can start an Invoice for Alice's
SuperWidget order, but Income:Expenses doesn't seem to be the right
offset -- it's more of an escrow.  How do I set up accounts to show the
order and then the subsequent transactions as the order gets filled?

Any help and suggestions would be appreciated.  Thanks much!