What is the markup on bikes sold in stores?
This can vary a good bit based upon the brand, quality of bicycle sold, and the agreement reached between the shop/brand. In general more volume=better deal, higher end=lower markup percentage (but higher dollar amount as the overall cost is higher as well).

A high margin would be 40-45% (66-80% markup), low end would be around 20% margin (25% markup) in my experience (as an employee). so for a $500 bike a 40% margin is $200, $300 original cost to the shop. In markup terms, a $500 bike that costs $300 wholesale is 200/300 = 66% markup.

Keep in mind this is not profit. Many bikes take an hour or more of labor to assemble, and this is before factoring in base costs of space, utilities, tools, etc.