How much should I charge to make this cake.
To feed 50 people. The base layer fruit cake and the top two sponge?

Presuming they're 6", 8" and 10" cakes, you'll get about 31 portions from the sponge cake (if you allow 2" x 1" portions) and around 68 portions of the fruit cake (if you cut into 1" x 1" portions).

Why not do do the top and bottom tiers in sponge, which will give you around 45 portions, and then do the middle tier in rich fruit, which will give around 40 portions.

Or the bottom and middle tier sponge = 54 portions and the top tier fruit = 22 portions.

As for pricing... Some people do a 3 tier cake for £250, others would charge hundreds more for a wedding cake. I'd say nothing less than £300, though. Maybe even more, as one of the tiers are fruit.

HI It looks gorgeous, I would say around £250 as there are only 50 guests, they may not want to pay more out, you could always swap the bottom tier to sponge and the top to fruit,