There may be cases in which multiple sub-domains under one domain need to be secured. For example, securing www.domain.com , orders.domain.com and service.domain.com under one certificate is possible with a wildcard SSL certificate.
Since you can secure an unlimited number of host names, wildcard certificates are generally more expensive than normal certificates, but they become very cost effective for those who need to secure several domains. Certificates in this category can range from $299 up to $800.