For under $100 your best off buying a used 3-5 year old camera. Probably no reason to have a camera that can do more than 5 megapixels. I have had pretty good luck buying used cameras on
ebay. There is a good chance that you will still need to buy a battery and a memory chip for it. Some of the cameras I have listed have sold on
ebay for under $40.
You should also have a small tripod.
The point and shoot cameras with the best macro lens are Canons.
Going back a few years the highest rated Canon ultracompacts are the SD950IS, SD870IS and SD850IS. Of the three, the SD870 and SD850 permit macro shots as close as 2 cm while the SD950 allows shots as close as 5 cm. Larger Canons also as close as 1 cm, G8, G9, S5IS, A650, SX100 and A720.
Might also want to check out the older Nikons Coolpix, 950, 990, 995, 4500.
Panasonic also makes some great cameras with macro, but I am not sure of the older model numbers. I am familar with the LX-3, LX-4 that have amazingly good macro lenses however even the old ones are pricey.