Add a s-tore to a already eisting blog, with different template. Necesito agregar una tienda electrónica a un blog que ya existe, con un templete diferente by welovesex

The page is WeLoveSex.com.mx is a mexican site and we need to add a store to the site, that will use a different template wich we aloready have, it should be accesible through the main site’s menu. Need help deciding if it yould be a subdomain or jst one more foder… (Budget: $30-$250 USD, Jobs: WordPress)