Time for building in Accessibility - RISE 360

We are just starting to look at building-in Accessibility into our Rise 360 modules.  I would really appreciate some views on any extra effort (time-wise) this incurs as opposed to building without and adding features at a later date.  Whilst I know that Rise has more features inbuilt, there are still changes I want and need to make to ensure we support accessibility as far as possible. 

Many thanks in advance