There are many user testing sites out there but they are expensive. In additions the users on that does those service does not represent the actual user of your site because those using the service is an experience (they do it all day) and paid user.
A better technique would be to get people on Amazon’s Mechanical Turk. And get them to install Screencast-o-matic and to send you the video of them using it. Be general in what instructions you give them. For example, use this site to find your favourite laptop to purchase. This will cost 1/20th the cost of those user testing sites.
If you are launching a new service you could find millions of bugs in your app but instead of fixing them all which might take you forever, just fix the ones where the users are having issues with. Many bugs will never bother the user.