Mary Berry's recipe uses:
4 eggs
8 oz butter (or marge - but using butter because it's a fancy cake)
8 oz sugar
8 oz flour
for one Victoria sponge i.e. two cakes.
Previous posters have said probably 9 sponges in total, so 2 eggs, 4 oz butter, 4 oz sugar, 4 oz flour x 9.
2 eggs: 40 p x 9 = 3.60
4 oz butter: 50 p x 9 = 4.50
4 oz sugar at 55 p/kilo (2.2 lb): approx 60p
4 oz flour at 53p/kilo: approx 60p
plus butter for buttercream - guessing at least 2 lb butter: 2.00
icing sugar for buttercream - again around a kilo?: 1.00
fondant icing (Lakeland): 1.79 - probably at least three packs required: approx 5.40
edible glitter: 2.50 - probably around 3 required: 7.50
Basic cost of ingredients around 25.00.
An hour shopping for them (at minimum wage!) 7.00
Making basic cakes - probably in total two hours: 14.00
Making sure they're level, putting together, butter icing between each: probably another 1 1/2 hours: 10.50
Fondant icing over top: maybe only half an hour? 3.50
Fancy painting and carefully applying glitter (personally by now I'd be reading to just chuck the edible glitter over the top and have done with it): around 2 hours?: 14.00
Around 74.00 to make the cake. And she's offering 40.00?????
Even if, as pp said, it 'only' takes you a day, and even if you took 'apprentice' wages (3.50?) that would still be basic cost of ingredients around 25.00 and 6 hours at 3.50 = 21.00 - totalling 46.00 which is Still more than grabby woman is offering.