Food is a very general market, so whereever you advertise you're staring at your target audience (everyone loves food) ideally I would advertise on sites that cater specifically to your niche audience though such as food websites.

Have you looked on www.big-boards.com? This site lists the largest forums online, there might be one related to your speciality.

http://www.epicurious.com/ (number 1 for "food recipes" in google) cheap advertising on that site!

http://foodnetwork.com (number 1 for "food" in google) advertising available on their site as well.

Also, try google adwords and link exchanges!