Asking for a raise, how do I go about it?

Situation is, I've worked for a small business as the office manager for the past five years, I've gotten one raise since I've been here and the claim they don't have any more money to pay me more, yet they are in meetings with radio advertisers to shell out $4,000 to do a series of ads. They spend probably $5,000 - $8,000 a year on advertising, but can't pay me more. I'm crazy busy at work, they've actually let a few assistants go and I'm doing their jobs and mine and barely staying afloat, the only way I can is by skipping breaks and lunch everyday and staying to do a 12 or 13 hour day occasionally when things get too crazy. I'm in the process of looking for another job, but nothing is panning out. How can I ask for a raise and get one?