Comparing twitter, facebook and adwords advertising based on price is not the correct way.
Three of them specializes in their own way.
It will trigger ad in accordance to users preferences. You can't control the demography. Instead you will have to choose the "Keywords" which are most appropriate.
This will help you target specific audience. You can choose the demography such as: age, gender, location, interests, etc.
It is similar to Facebook Ads. But there are subtle differences like you only pay for user actions that are associated with your campaign objective.
Twitter ads are new and they improving it, working hard to offer a better advertising platform.
Yes, you can plan and divide your budget between these three as per the reach you are expecting.