@ieales: You have the markup formula correct, but the nomenclature incorrect. Wholesale is the price the retailer pays the manufacturer (or distributor) for a component, which in hi-fi is typically 60 points (percent) of the retail list price. So a piece which retails for $1500 typically costs the retailer $900. The $300 figure you cite is correct (for a component which retails for $1500), but that is not referred to as the wholesale price, but rather the cost to manufacture a piece of hi-fi gear (there may be a more technically specific term for that price, but if so I’m unaware of it).
The difference in price between the cost to manufacture ($300 in this example) and the wholesale price ($900) is the amount the manufacturer (or distributor) makes ($600), the difference between wholesale ($900) and retail ($1500) prices what the retailer/dealer makes (also $600, assuming the component sells for full list price).
However, in some product categories (cables and hi-fi "tweeks") the cost to manufacture may be far less than 1/5th the wholesale price. That’s one reason those items come under such harsh criticism from the "skeptics". The creators of such products defend their pricing in terms of the man hours that were invested in developing their products.