It's actually really easy. Ready? Don't write a long list to start with.
Sounds partly too simple, and partly to have missed the point, right? Well, it is neither, I promise. When we wrote our guest list (having realised we need an idea of numbers to do the venue search), we just wrote a list of the really important people. Immediate family, close friends, people who've been there for us throughout our lives. The total was (roughly) 50. Job done.
Yes, there will be separate evening guests (not too many though), and there are possibly a couple of people who may get added. But that is all. We won't be inviting colleagues (because we may be unemployed at the time), or cousins who we haven't spoken to in years, or friendships that are limited to Facebook. We're really happy with the list, and (amazingly) so are both sets of parents.
There is a caveat. We have chosen not to invite our guests' children. This is because of our original priorities (number 4 on the no way list was a party overrun with kids), and the fact that there are so many of them. We are just having the four children in our immediate family. We have sent an explanatory note with our save the dates, so hopefully everyone will be able to find childcare and use our wedding as an excuse for a weekend away, and no one will be upset with us.
Note: the details of the budget are coming soon, but blogger has eaten my awesome chart and I have worked 6 days out of the last seven - when work is a 12 hour shift plus travel - so I haven't had time to redo it.