Determining how much a website should cost is one of the most frequently asked but rarely answered questions in the web design community. In today's world, even with millions of websites that exist online, there is not a single accurate(!) formula for calculating either the cost of a new website or the cost of a redesign (CMS-based or otherwise). But we wrote an article on this: https://webdesignandcompany.com/how-much-should-a-website-cost/