I do believe that this is the worst approach of deciding the technology used for a project. On a generic perspective a designer is cheaper than a programmer, but sometimes, a designer can loose 10 hours on something that a programmer could do it in 1, and vice versa.
So, if you need a simple slideshow page, or a small animation with no smart functionality, maybe HTML5 is the best choice. If you want something more complex than Flash might be a solution.
And please, never decide the future of your project on the cheapest solution, there are plenty of reasons on why a technology might be the best choice.