I am developing a "Mount Vernon style " garden,,need an affordable source for perennial herbs in large numbers
Seeds. Seeds are the most affordable way to get large numbers of plants. Be sure to check out winter sowing which allows you to start large numbers of plants from seed outdoors in the winter. My indoor seed starting space is limited, as it is with most people. But winter sowing gives you other options and oodles of space. It also takes care of any seeds requiring cold stratification naturally.
What herbs exactly are you looking to grow? It helps to know to suggest sources.