If it's just two guys with acoustic guitars in a quiet bar, the 200W setup would probably work fine. If you've got two Les Pauls going along with a bass, vocals, and drum kit in a busy bar, you will need considerably more power in order to be heard.
I'd start at 1000W minimum for what you've described, and double that if you can afford it. The thing about volume is the louder you get, the more power it takes to get even louder. It's not a linear thing, it's logarithmic. So it takes an order of magnitude more power to get from loud to really loud.
And Joey makes an excellent point. Used deals can be had everywhere. Craigslist is your friend here. Just check the retail price of anything you might buy (scammers on Craigslist? Nowai!) to be safe.