So, you're a writer and you've just finished your script when you remember that your drawing teacher gave you a "C" on the condition that you never EVER take a drawing class ever again. This means that you need to hire an illustrator. You then check your wallet and bank accounts and quickly find that you just don't have the funds for a bowl of ramen, much less an illustrator. So, what can you do to afford an artist...?
Find a college student. All right, let's get the obvious one out of the way. The sad reality is that there are few illustrators that can also tell a story. Sure, they can draw a pretty picture, but story-telling requires an entire different kind of artistic sense; you are juggling an entirely different kinds of metaphors, relationships, and issues, and not all illustrators can juggle those at the same time as the more visual ones. However, the industry requires portfolios that not only come with gorgeous pictures but also a decent story. So, with a little luck you will find an illustrator who is looking for a writer and you can team up.
Discuss split profits. Before the illustrators get too ticked off me (again), a proven writer can pull this off. It means coming up with a marketing plan as well as a killer script, and approaching an illustrator with all of this. It means that they had both better be darn good or the illustrator will probably ask security to do something about getting rid of your sorry butt. So make sure that your script really is top notch and that your marketing reflects reality not fantasy.
Max out your credit cards. This is a time-honored tradition in the movie business. All you need is a great credit rating and a few decent lines of credit. If you can pull that off, you just need to determine how much you need, and then arrange a loan via your credit cards. How much does a comic cost? Figure $150-$250 a page (depending on if it is colored or not) and go from there.
Barter. Find out if the illustrator has any particular needs and promise to fill them. Ignoring anything illegal, this can mean room & board, a studio for other projects, repairs on his home or vehicle, or some other need that has to be filled and you can take care of. Feel free to be imaginative if necessary, but if you can find something he needs you may be able to get him to exchange artwork in exchange for it.
Kickstarter (or equivalent). Write up a proposal, determine how much you need, decide on some basic incentives (such as a printed version of your comic or guest spots), and then find a way to advertise it. The idea is simply to find an investor and then make sure that the investor is paid off. If you can pull that off, you should be good to go.