Too wide a question Bigbet, it depends on the business. While Joey is probably talking about Restaurants which in England they see 1/3 of takings going in overheads, bookmaking can be 0.08 of turnover.
You could reverse audit the business and ask how much is it worth then summise the labour costs but more to the point is how much the going rate is in other outlets, maybe you find the staff cost is more in your company but you have better staff.
When I was in business I made sure I paid top dollar, that way I always had the best service. If there's a problem then its nothing to do with staff service. :thumbsup: