Don't think there is a cost for putting your listing on Trula. Either your company has syndication (feed) to Trulia, or you can submit your listing via the 'submit your listings on Trulia' link.
Other services such as vflyer and postlets feed into Trulia also. .
Although Trulia does charge for putting your listing as a 'Featured Listing' - there is a pricing structure for that. You need to contact their customer service.