Magnetic whiteboards are extremely expensive to buy at office supply stores. They are made from something called “porcelain steel” or “porcelain on steel”. The steel is what makes these whiteboards magnetic. Magnetic whiteboards often cost 2-3 times what regular non-magnetic whiteboards cost.
As others have pointed out here, you can buy regular non magnetic whiteboards for 1/10th the cost by buying melamine sheets (also known as shower board or tile board) at any major home improvement store for around $10 a sheet.
One way to transform these non-magnetic melamine boards into magnetic whiteboards is to back them with something called rubber steel, or flexiron. This rubbery material typically costs around $3 a square foot. The material is easy to cut and can be quickly attached to your sheet of melamine by applying an adhesive. Shouldn’t take more than 5 minutes.