The bit that struck me right from the start was, the OP said she wanted a 3 tier cake to feed 50 people. Wow that's a lot of cake.
Then OP'er said she was going to make the tiers - 6'-8'-12", and again that is a lot of cake, for 50 people. The 12" alone will serve over 50 people.
The OP'er needs to do more research than just pricing.
And as a side note, I didn't think anyone was rude, except the OP'er.
Also that cake looks simple, but it will be time...