I own and operate a small business not related to the martial arts, It's a retail store that caters to the medical community... when I began I had no money for a commercial location, and tons of inventory, let alone advertising. So I attacked my target market with flyers. Hospitals, doctors offices, dental offices, clinics, etc... word of mouth within' those communities spread quickly and luckily, I didn't have to dump money into the news paper, and telephone books. (In which case, you're spending money hoping somebody will find you, with flyers, you can target anybody you want directly via their mailbox, posting in schools, churches, windshield wipers etc.)
I DO however agree with the comment that you do need a website though - in this age of technology, more people will be looking there before a TV ad, radio ad or flashy newspaper ad will jump out at them.
Also, you may be sitting right on your location and not even know it... A church gymnasium that's not being used during the week, your child's middle school multi purpose room, or you may know of a local gymnastics academy or dance studio, who has an extra room or a few nights a week that they're closed where they'll let you use their facility - you could compliment each other greatly, the child who isn't good at tumbling may find martial arts more appealing, or students might take both. You'd also have an entire crowd of parents and siblings who would see you and say -
"Hey, what's going on in that other room?" or "What's that sword on the wall?"
"Oh it's a martial arts class that practices here tuesdays and thursdays, talk to Jade Cloud, he's an awesome teacher, many of gymnasts and parents take self defense classes with him."
or in the case of a church "Our entire men's bible study group and teen group is thinking about joining and taking your class on tuesdays and fridays when our women group meets up, because we don't have anything scheduled for them."
Just some ideas, hope it helps! When you do get kids to enroll - encourage mom and dad to take class too! Sometimes they might need that extra motivation to transform from a Karate mom/dad who sits on the bench to an active student who is working with their kids, it'll strengthen the fabric your MA family and theirs as well.