I’ve done this before. A huge advantage is that in addition to being cheap, you can tape the bait traps anywhere you want – out of sight for the Martha Stewart types, away from little kid’s hands for parents, away from curious pets for pet owners etc.
Boric acid is a white powder, and I’ve found it in every big-box hardware store and most bigger-big-box grocery places with the other ant and roach killers. You’ll need:
[ul]
[li]boric acid powder[/li][li]mint jelly[/li][li]disposable drinking straws[/li][/ul]
(Why mint, I don’t know, but the person who gave me the recipe – and the exterminator who taught it to her – swear by it. I’m sure any sugary fruit jelly would work, though. Should probably skip the sugar-free kinds, since it’s the sugar that attracts them.)
In a small bowl, mix about equal parts of the jelly and the boric acid with a toothpick or other small disposable implement. The jelly will go from being clear and dark green to the appearance of toothpaste. NOTE: they are not interchangeable! 
Snip a drinking straw or three into lengths of a couple of inches, and use the toothpick or a Q-tip to stuff a little of the boric acid mixture into the ends. It’ll be kinda gloppy, and won’t look neat, but it’ll hold enough of the mixture to slowly but surely poison the ants and, more importantly, poison the queen they go back to feed.
Tape the bait traps wherever you see their trails, near potential openings or food sources. Some folks say it’s good to put some in the bathroom, too, since ants and other insects often invade homes for water and/or shelter and the free food is just a bonus.
Now, here’s the important part: be patient. You will inevitable think they’re not working, at first. Then one day you’ll realize you haven’t seen an ant in … well, not in a while. Huh! Guess I owe purplehorseshoe a thank-you gift!
(I accept cash.)