I'm an amateur who does perhaps one or two cakes a year for family since I started learning for fun eight years ago. So I can't say I've had that much experience...
Looking at the beach cake, it shouldn't be that hard to do. The chairs and table are run-outs and lace trellis work, which takes a bit of time but not that much, and perhaps the shells are real? The rest is just fondant with sugar stuck to it. The cake may be just a cube shape on top of a dome (probably in madeira sponge) covered with marzipan then with the fondant being the shaped part.
I'd have trouble with the figures though - not done many of those! I suspect the biggest cost for the whole thing is due to the sheer size. It looks massive.
Wish someone would give me £500 for one of my cakes...