I work at a web design agency about that size. Good luck finding any budget for testing. Clients don't care, and if you budget for it most will go with a lower bid somewhere else.

As someone else said, it's basically account people clicking around, you fix stuff, they click more until they feel comfortable presenting it to the client. Then you find out that some bigwig at the client has a 5yr old blackberry where the layout doesn't work right, and that becomes your focus of your debugging for a week.