How Much Should I Charge Companies To Advertise On My Website?

This is entirely up to you. If it is costing you a significant amount of money to run your website, then you obviously want to charge a fair amount so that you'll have enough money to invest some back into the site.

Some sites give companies the option of advertising quarterly, monthly, for half a year, anually etc. It's up to you how you arrange your months for charging companies. Some sites also charge companies more to have their advert in a really obvious place on the site.

If you are running the site with someone else, then discuss it with them and see what they think. If you decide against advertising, then you could always sign up or Google Adsense, which allows Google to advertise on your site and you receive some money each time an item which is advertised through your site is purchased.