Generally speaking, what is a rough figure on a per-character basis for lineart (single character,  not scene)? We talking 50-100? Or is the going rate larger? (hopes not)

It varies alot. ALOT.

I suggest that you contact artists that you're interested in working with and ask them their rates for such a project.
Or decide on a rate that works for your budget and post an open call.

Good luck with finding the right talent!

It's not only according to the artist's ability but also what the image will be used for.  The lowest possible rate you can get is probably $10 for a quarter page figure. If you want something of the same quality you see in comics, it would cost $100 for a full page or $25 for a quarter page. I suggest the same thing as devilbunny, look on some art forums and find somebody you like and contact them about their rates. Here are some forums where artists hang out . conceptart.org ,rpg.net, deviantart , drawstick, sketchkult,gutterzombie, penciljack

thanks for the info. I'm very very picky on what I want.... for this particular book I want an original feel withotu the usual recycled feel to the artwork (fantasy game). I'm aiming for a cartoon/comic look with a heavy burton-esque flavour. Not many artists out there that meet the requirements:)

The lowest possible rate you can get is probably $10 for a quarter page figure. If you want something of the same quality you see in comics, it would cost $100 for a full page or $25 for a quarter page.

Troy,
Buying stock art is very different from commissioning original art.
So the price difference between the two options makes sense.

Sayter,
I would highly recommend using the Freelancer's Forum  on rpg.net to find illustrators. State what you want and what you're willing to pay and I guarantee you'll get some informative responses.

All the best!