|I figure since you mentioned AT&T you're in the US (I'm in Canada) so I did a quick search for a big US electronics company and came up with Best Buy.|
I did a quick search on their website for wireless routers and found:
I had a quick look through the list keeping your "Under $100" restriction in mind and found the following:
That fits your budget and would do what you need to do.
You could find something similar in any computer store and most any other big electronics chain.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.