http://fiverr.com/

And at the time of this posting, on the main page there is a guy who does voice-overs.

But, for the final recording, you cannot ask each person independently to record themselves without having bad surprises.
You need at least to record everybody using the same mic and then do a volume calibration (the "mix" if I translate the French).

What I would do if I was in your situation is searching for a close university doing audio-visual studies to find a student to do the recording, they usually have good material and sometime because of their teachers or their student projects, they have contacts with actors.

Yeah, unfortunately, with me being in London, recording studio's likely to be incredibly expensive... I know there were a couple of decent places for cheap near where I studied. The issue is that I have absolutely no knowledge, or experience, in getting voice actors. I also don't have an awful lot of time to run around London arranging auditions and stuff, which is why I stuck it online. If I get enough people near London, I can look into a recording studio, otherwise, initially at least, I'll just have to make do with whatever audio they can provide.

I'm trying to balance quality with potential costs, as I know the lower the amount I ask for, the more likely it is that we can achieve the funding, especially as none of the team are well known in any way. I'll just have to see what kind of things are available and what sort of budget I am left with, to spend on things like professional recording.

I have some experience in sound and voice recording for games and films with contacts (in France only), if you want I can ask informations about the cost.

But basically, what is the most expensive is the studio recording (same if you need special sound design), actors are affordable and non-professional can be very good. Non professional recording can however ruin your game.

I have started an "audition" over at voiceacting.co.uk (I hope noone minds the cross post) and asked people to submit samples of their work, and how much they thing they would like to be paid, if they got a role.

I posted, basically on a whim last night, after failing to get any decent rates from websites and have already had several emails back. I just thought, as this is the community I spend most of my time in online, it would be polite to make everyone here aware of this. Maybe you think you have a voice that might suit one of the characters, or maybe you know someone who might want to do it. Anyway, the link is here again. If you would like any more information, just give me a shout