Cost of Logo Design services

I'm trying to work out a budget for a start-up of mine that I'm thinking about, and I'm stuck when it comes to graphic design.

What I will need designing initially is a high quality logo, I'm not looking to cut corners, because I'm planning to retain the business myself for about five years, and would hope it would last that duration before the business is passed on. What should I look at budgeting for this?

How do I determine what other elements of corporate design I will need, such as letterheads, business cards, and is there a large additional cost to this? N.B. It is a service orientated busienss that I would be starting and would operate largely over the web.