The cost to attend a webinar depends on how much the organization (that is hosting the webinar) charges. The organization hosting the webinar will (often) calculate the cost they charge by determining how much they have to spend to host it. Also, if the organizing party is having a special guest speaker(s), the speaker(s) might charge the organization for participating in the webinar. Finally, the organization hosting the webinar will often use the size of attendance to determine how much to charge. For example, if the cost of hosting the webinar is large, but they expect a large number of attendees, then each attendee won't have to pay as much to cover the expenses. However, if the organizing party incurs a lot of expenses, but they don't expect a lot of participants, unfortunately, the attendees could get stuck paying more. In short, the best way to determine the cost of a webinar is by asking the organizing party how much it will cost.