Do a load calc, and quick layout then come up with a "budget number", nothing fancy just a number you feel is right that will include plans and a seal if they need one along with some profit and overhead for you.
Then give them the budget number with a clear scope of what they will get for that budget:
1) Plans
2) X number of receptacles.
3) Fixture allowance.
4) Fire Alarm (if required).
5) XXX size service.
Do not give them a set of plans back, do not spend too much time developing plans, just do enough get budget number.
Once they agree to use you, get a contract for developing plans, and doing the work. Then as you work with them developing the plans you can keep them on budget or you can get paid for a change in scope. As a design builder it is your responsibility to keep the job in budget or make changes that both of you can live with.
Put your salesman hat on and go to work, if you do it right everyone will be happy.
BTW I hate doing churches, its really hard to make any money on them.
