Since you will be using this actor to get financing, they become
primary partners in the production. Without them, you can't get
the money. So you aren't actually making an acting offer, you are
asking for their help in financing.
Keep in mind that any actor worth having attached to your script
is already getting a stack of scripts from producers and studios. Also,
this is what they do for a living. Many are willing to help out a low
budget moviemaker, but this is much more than a hobby to them.
Working for the ULBA or on deferred pay takes them off the paying
market for the length of your shoot. And you have to stand in line:
First on the list are offers at or above their "quote". A guaranteed
paycheck.
Second on the list are scripts from studios and producers for less than
their quote - but these are also firm offers (money is attached, they
get paid when they say "yes"). These are projects where the script
may be more important than the money - but there is still money
(and often a high profile writer, producer or other actor) attached.
Third in line are pet projects. The actor has a pet project they will
take to producers with no money attached, but it's a story they really
love.
Fourth in line are scripts from friends or friends of friends. No money
attached, but at least brought to them by someone known to them
personally.
Eventually we go all the way down to some total stranger with a script
and no money. Imagine the odds of doing that script instead of any of
the others?
Knowing that you are number five on a very long list of scripts being
offered should help you decide how to approach them or their agent.
Maybe you could offer a producer credit to the actor, or a good friend
of the actor.
Then there is the fear that their name might not be enough. You need
their name to get financing. What if you don't get the money? Nothing
happens to YOU but they become the actor whose name wasn't good
enough to raise money.
It CAN be done. It HAS been done. Understand the business and what
the actor will get out of it and that will help you approach them in a more
professional way.