wow. I'd say you really need to get someone knowledgeable in to actually look at the space and help you out. It's really tough to ballpark figure without seeing it.  It's going to be a big number but I'd hate to even wager a guess.

I say bring on the experts and get as many quotes as you can - then you can realistically approach the project, and see if you need to break the project into a graduated plan of attack.  One thing I will say - get more power than you think you will use, and a lighting board and dimmers that currently exceed the number of lights you have.  You WILL gain lighting instruments, and if you don't have the control capacity, 50 more circuits really don't mean much. 

I don't know where to begin to find a theater designer.  We're near Morgantown, WV.  We don't have any money to even bring in a theater designer consultant.  That's what the grant will do, but how can we know what we need without the consultant in the first place?

I'll concur with Brad, you may want to refocus the grant application to address just a feasibility / programming study.  A team of Architects, Engineers, and a Theatre Consultant are trained and experienced at this type of project planning.  Spend a little money upfront to get the project going the right direction and you'll be able to more fully understand and communicate where you are going and how much time, effort, and funding it will take to get there.  Many Architects and Engineers have told me that building a Theatre is the second most difficult type of project (a hospital being the first).  This is because there are so many minute details that affect the outcome.  Every component of the theatre affects the audience and/or the performers and/or the support crew, so seeing that they are all carefully coordinated and defined is very important.

Don't be too concerned about not having a local consultant, most of us travel all around the country (and sometimes the world) to serve our clients.

With regard to 'bring in some experts and get some estimates' . . . this is a slippery slope.  This usually implies bringing in vendors / contractors, and their vision may be a bit too focused on the short sale rather than the big picture.  All of the systems in a performance space are inter-related, so individual product vendors may not communicate all of the ancillary support elements that are needed to implement their part of the project.