At the moment you can only enter "financial mode" on a listing which means you cannot attach any sort of proposed budget to a potential listing - this must be done externally from REX - which means you create it somewhere, then if/when the property lists you need to re-create it in VPA to be able to send out a Funds Request.
I think it would be very helpful to be able to create potential budgets in Property Mode so when you list they are there ready.