Bay ridge nursery sells rocks. They are very good people. I really like them. If you are pretty close to them they will also deliver free.

Irwin Stone in Rockville has 3 sizes of river rock for about $75-95 a ton. They deliver everywhere. I bought a 1/2 ton each of the middle and large size. Here is link to my pond to give you an idea of how much a ton is. The "after" pictures have the river rock surrounding everything. The other rocks are what we got out of the dirt while digging the pond.

Here is a link that might be useful: my pond