Susan, I forgot to mention
(for some of the rest of the membership, as I am sure you already know) that it also depends on the species of finch that is desired to co-habitate with the budgies. I already know you have a Society
(soon maybe two or more - lol) 
, they of course are not as territorial as some finches and have one of the best chances to work out with the budgies. Of course one would watch how they get along
(for a long enough period of time) before deciding to leave them together in a large flight. The other usual rule comes into play here also which is best to put them into a new large cage together rather than one the budgies have already claimed as their territoy.