Buy an organic beet. Should colour pretty much anything a nice bright fuchsia (I've used it in frostings and potato salad on purpose, and on other things by accident). Or blackberries and raspberries, although depending on the acidity of what you're making it might end up purple rather than red.
Otherwise I would just start checking around the internet for a good deal. You'll probably still end up spending $10-$20 on a color kit (looks like single colours go for about the same, as they come in larger quantities).