I am curious about the average price for a 6, 8, and 10 inch fondant cake. Also, I'd like to know the average price of a 2 tier cake with a 8 or 10 inch base and a 6 inch cake as the top tier. Thanks!

that's gging to depend on where you are; how complex the design is and how far the delivery is....
There is much that goes into pricing as you can see. Pricing varies from big city to very rural village; from one county to another or state to state.

Our pricing for a basic single tier 8" cake covered in fondant starts at $74, or $84 for a 10". (We don't advertise 6" cakes, but we will make them for the same price as an 8".) Our multi-tier cakes start at $5/serving. This is in the SF Bay area, and California requires a licensed commercial kitchen so the prices reflect that increased overhead.

Of course this won't help you much if you live in a different area.