Keep in mind it was NOT an all or nothing proposition for using the Shuttle. We launched satellites while the shuttle was running using Titan, Atlas, and Delta rockets. I would imagine if it was more cost efficient to use those rockets, they would have done so.

https://en.wikipedia.org/wiki/List_of_Titan_launches and https://en.wikipedia.org/wiki/Delta_IV and https://en.wikipedia.org/wiki/Atlas_V