That cheapest isn't the best answer ever because a good quality is that you can't worth in $100. Or on the other side the used furniture is cheapest but it won't last long. In my recommendation Sofa Paradise Furniture that I use to shop for is the best place to buy good quality at low rates.
http://www.sofa-paradise.com/dining-room...
Check out your "Habitat for Humanity" local chapter. They usually have a warehouse store where they sell donated furniture and construction stuff for super cheap.
"There is hardly anything in this world that some man cannot make a little worse
and sell a little cheaper, and those people who consider price only, are this man's lawful prey. It is unwise to pay too much, but it's worse to pay too little. When you pay too much you lose a little money - that is all. When you pay too little, you sometimes lose everything, because the thing you bought was incapable of doing the thing it was bought to do. The common law of business balance prohibits paying a little and getting a lot; it cannot be done. If you deal with the lowest bidder, it is well to add something for the risk you run, and if you do that you will have enough to pay for something better"
John Ruskin (1819 - 1900)
Buy Chinese crap for $100 and it won't last a year. As suggested, look for a quality used piece from Craig's list, estate/yard sale, or auction.
You're going to be limited to thrift stores and Craigslist if you're looking for something for $100.
Check freecycle.com for some finds that usually involve only the price of gas to go pick them up.
ikea! or ikea.com
I want to buy a dining table for less than 100$ in southern California more specifically the San Fernando valley. Anyone know a good and cheaply priced furniture store? I've never bough furniture before. Thanks.