If you can’t afford a regular whiteboard that you see in office supply stores, you can actually make your own whiteboard at home, and it is much, much cheaper. You will spend about $20 as opposed to $100+ per board.
First, you need to consider the size of board you would like. It comes if 4’x8′ sheets, so if you do not have easy access to a saw, it is easiest to have your whiteboard at that size. If it is smaller and you do not have access to a saw, you can ask the building supply store to cut it for you, but be aware that there may be a cutting charge and you may still have to buy an entire sheet, even if you do not want all of it. They also may not be able to cut it as specific as you want – if you want it 25-3/4″ wide, you might end up with as much as a 1/2″ difference either way, and it might not be perfectly straight. So you will need to keep these things in mind too.
Once you know the size you want, go to your local building supply store and purchase melamine. It is fiberboard and one side is coated with white shiny surface. There are new decorative melamine surfaces out there, so make sure you are getting the smooth one.
To mount to the wall, you can attach it with heavy duty mirror hooks, screws, picture hangers or even glue. Once mounted, you can use it just as a dry erase board. Only use special dry erase markets on it. If you need to draw lines or grids semi-permanently, you can use pin striping from an auto shop (what they use to pinstripe vehicles).