What's the best wine to order in a restaurant if I want bang for my buck?
Beer. (Just kidding.) It depends on the establishment, but there's something to be said for choosing the offbeat. Restaurants can't afford to have inventory collecting dust, unless we're talking about trophy wines that get more expensive as they collect dust. Wines made from uncommon grapes or wine styles that simply get little attention usually have been priced to sell. This can include oddities like ribolla from Italy or piquepoul from France, and it includes appellations like Toro in Spain.
It can also include something as familiar as Beaujolais, the red wine based on gamay, simply because there's not a lot of demand for Beaujolais. (I often choose Beaujolais because it's food-friendly, refreshing and usually well-priced.)
Why would a restaurant carry wines few people drink? Because of the sommelier. These wine experts, who control or assist in the buying, want to keep things interesting. They also want to carry selections they believe will pair well with the chef's food, and that may mean stocking up on Corsican sciacarello even if nobody's heard of it. Usually these wines are a point of pride for sommeliers, and the restaurant is likely to price them well because the sommelier wants people to share his or her enthusiasm. A restaurant could get by just selling wines based on popular grapes, such as cabernet sauvignon, chardonnay and pinot noir, but what fun would that be?
Obscurity is no guarantee of value, of course. Some restaurants calculate a fixed percentage markup regardless of the bottle. But you're more likely to get gouged by pinot grigio than gros manseng.