I'd say about $7-8 is the point at which I'd probably have to think about it, might get it later or not at all.
Mind you, I thought the beers were rather mediocre at a brewpub in my parents' town, was curious about a glass, and I believe they were charging well over $10 for non-shaker glasses. Under $8 for a glass from a place that sells really good beer, I would much more readily pay. How much I like the beverage definitely would influence my decision to buy a glass!