@thatsallineed
I must be missing something here. The ingredients for a nice 8" sponge cake plus fondant icing would be not much more than a fiver.
I'd want gold leaf on it for £70.
The ingredients for a sponge might be a fiver, but given it serves 25 it must be tall, so that'll take loads of buttercream, which is expensive, easily £4 just for the butter then about £4 for the icing sugar. Fondant, if its tall, probably about £3-4 for the plain white ready made stuff. More for coloured - even if self-coloured as the gels aren't cheap. Then a sturdy cake board - not a flimsy supermarket one, and a box to put the cake in.
I'd say £15-20 without factoring in any decorations. For ingredients alone. I do know, as I made a cake for a friend lately (not for her, but for her to give as a gift) and I costed up ingredients because I made it as a favour but she had to cover costs. Hers was dearer as it involved a few colours, so about another £5 for colours gels.
Then if you add up time to cook several cakes for layers, clean up after them, make buttercream, crumb coat them, buttercream cover or fondant cover them clean up after all that. That's at least 3 hours. Any decorations would be extra time. So even just 3 hours at £10 is £30. But £10 an hour is a low wage for a skilled creative task like that so really it should be more.
So £45-50 so far, for the main ingredients but no decorations plus cheap labour. Decorations would obviously take more time as well as ingredients. Far above what you're scoffing at 'barely more than a fiver'. A proper baker will also need to cost things like rent for cooking space, utility bills, equipment cost, insurance, time spent conversing with customers, buying supplies etc into their business model.
Some people really have no clue as to the value of a bespoke cake.