In my work with both game development and contract animation, I often find myself in a position where I have to argue for paying for voice acting. For some reason, clients seem to feel that voice acting is something anyone can do ("can't you just do it?"), or that it's an easy skill (and therefore shouldn't be expensive).
Conversely, I've met quite a few people wanting to be voice actors, and expecting to get work just because they have an USB microphone and a laptop.
Good voice acting is difficult. And it's totally worth the cost.
I was just reminded of this by the game Gun Monkeys from Size Five Games. The game itself is a pretty cute competitive side-scroller about flinging monkeys into the future. They brought on The Actor Kevin Eldon to narrate the game. It was a great move -- his voice takes the game to a new level, adding personality and charm throughout.