Larger tears in canvas paintings will require lining - an addition of a second canvas to the reverse using a proper lining adhesive. Beva 371 was originally invented by Mr. Berger in the late 1960's as a way of lining bright, colorful modern paintings without darkening and changing them. Research and Innovations by Gustav Berger and William Russell, recently published and now available from Talas . All of the above takes time. And it takes time to do well.
Conservators charge by the hour.
Now if the frame needed some work, there was some cracking or staining that required extra time or the oxidized varnish was on top of a dirt layer, or the varnish was crosslinked, or etc. Scientific analysis will have to be undertaken along with research by specialists and art historians. These major treatments can easily cost many thousands of dollars. However, there are no shortcuts to an adequate conservation treatment. Somewhere along the line a lot of time, effort, experience, and expertise has to go into the actual treatment if it is going to come out well.