If $200 is your limit, I'd go with something around 40 watts. These are both good options.

Here's one from RMS: http://www.amazon.com/RMS-Watt-Acoustic-Guitar-Amp/dp/B0015GTOSW/ref=sr_1_35?ie=UTF8&qid=1437005537&sr=8-35&keywords=acoustic+guitar+amp

And an Acoustic A40: http://www.amazon.com/Acoustic-A40-40W-Guitar-Combo/dp/B00PWMQ75I/ref=sr_1_26?ie=UTF8&qid=1437005522&sr=8-26&keywords=acoustic+guitar+amp

It'll be hard to get something with anymore size in that price range.