Gradar1, as with most things in life, everything has a price. Disney will tell you what that price is for each of their venues. It is up to you to decide whether or not that price is too high to pay. It is a very personal decision that only you can make.
For example, Venue "XYZ" has a minimum price tag of $100,000. For $100,000, you can have a very nice party for 100 people. However, if you only had 10 people but you still had $100,000 to spend, you could hold your event in Venue "XYZ" and have one heck of a night to remember for those 10 people. I hope you're following my analogy here.
So, if you truly want to have your party inside the American Adventure, ask your Event Manager exactly what the barebones minimum cost is. If you can live with that cost for a small guest list, then by all means book that venue. But if you think that cost is too high of a price to pay, then ask for alternative venues that might give your wedding a similar feel but for a cost that is more inline with your budget. Your Event Manager is a wealth of knowledge. Don't be afraid to tap it.
I had an incredibly magical night inside the Disney-MGM Studios Theme Park. There were only 22 people at my event. Yes, my event was pricey, but it was a price that I was willing to pay. I truly had the most magical night of my life, and I will cherish my memories always. If you can dream it, Disney can make it come true.