Hi Zinnia Love,
I would be leary of the Dollar Store. I got all of my art supplies, including brushes, in the art department of a hobby store. Nowadays I might buy art supplies from Amazon. But dabbing zinnia pollen isn't critical. I have on occasions used the tip of my little finger when I didn't have anything better handy. As a different way of doing it, I also pick the florets themselves with tweezers or forceps and rub the florets on target stigmas.
ZM