Making an Egg Cream at home is really easy and inexpensive. To give you an idea of cost, I used to go to Lindy's for lunch sometimes when in New York. It's in midtown Manhattan across from Penn Station/Madison Square Garden. An Egg Cream there cost $6.50. Other days I would go downtown to Greenwich Village for a pastrami sandwich at Katz's Deli. An Egg Cream there cost $4.25.
Here it is:
First put milk in a glass. About 1 ounce.
Add seltzer, A head will form. Gently, without disturbing the head, add Fox's u-bet Chocolate Syrup, and stir. The head will be white but not for long. An egg cream is meant to be consumed immediately!