You can definitely get something worth riding for $200 if you have some mechanical skills. I'd look at craigslist and find a vintage MTB with a rigid fork; figure at least a new pair of tires into the price as you will want slicks. You can do this for less than $200 and have a bike worth keeping.

Edit: if you post where you live and put up a posting on C&V appraisals, people will help you pick out which bikes are worth buying in your price range. Vintage MTBs and hybrids don't tend to go for much and make first rate commuters.