How do I add text options to post

A client of mine is using posts to display his products for a rental business, and he has asked me to add two option fields within the post page so he can put in the weekly and monthly rental price for the item, does anyone know a tutorial that I could use to do this?

I have been looking for answers but they all point me to the custom field option, but I would like to try and have it coded in as its own box within the post page.

I hope that makes sense.