Here's another study that showed that yarrow (Achillea millefolium) has repellant properties. I also read about thyme, and have some I just harvested, and have read multiple reports of white vinegar being a repellant (and that could be a base, cheaper than alcohol).
I've been using pennyroyal from the garden, tinctured in vodka, then diluted in a spray bottle, for years with success against all biters. Needs reapplying once an hour or so, but as a bonus it smells nice and is cooling. I always spray my hat and clothes, too. And when we owned a camp near a swamp, I accidentally discovered that eating tons of pickled ginger kept them from biting. May have had something to do with the vinegar?