So we spec it for a one hour window/one time only ever demand, for appointments made weeks down the track. If you log on today rather than yesterday it makes no difference? I would imagine that's a bit of a waste of money and resources, although I am an accountant not an IT boffin, it may be cheaper and easier than I know.
You decide what you want to spend to handle your load. If you decide to lower your costs and let your target audience face some disruption during peaks then it's your call. Commercial entities would rather not have the bad press as they would lose customers to competition. Monopolies or Government depts wouldn't care too much about losing customers.
How easy is it? You log into a portal and click a couple of buttons and there you have it. Sure, you may go over budget but that's the accountant's problem, not the IT dude.