I know this is MN and everyone is wealthy but would peope seriously order a pizza each from takeaway if they had 25 people coming over? That could easily cost £2-300! Plus cupcakes. This is just a social evening, that's a lot to spend on snacks.
Not a pizza each, but when we throw a party, yes, we spend about £100, about £50 on pizzas from a takeaway (usually 1 per 3 people), and the rest on snacks, puddings, breakfast food for the overnight guests and most importantly booze!
I don't think £100 is an obscene spend for an evening's entertainment for 25 people - £4pp, much cheaper than a night out! People usually also bring booze, so we 'reclaim' about £20 that way.
Maybe it's the fact that you've never done it that means you're overestimating?
(I insist on takeaway not oven pizzas because even though we've got a big double oven, it comes out in miserable slice-per-person quantities that way, and unless you're serving a group you're not a part of, it means someone stuck not enjoying themselves)