How to calculate pricing for logo design

I’m sure people on this forum are getting sick of these questions, but I have no idea and I need help.

I’ve been asked to give a quote for a logo, I think the client is designing his own site but is stuck on the logo. He only wants something simple, and most likely in black and white.

I usually only do whole sites, and I always get worried that I’ve over/under charged.

Any help or suggestions are appreciated.