Wireless internet help?

I have a Macbook and almost every time I go on the internet (wireless) I'll have 1 out of 4 bars, or zero bars. I really want something to stabilize it on four bars, whereever I go (not just in the house like some wireless routers). And I also want something that can plug into the side of my Mac for preferably $100.00 or less. I will give best answer to the person who finds something that works for my Mac!!