Not that I've been to a (more formal style) folk club in years my main reason for going to one would be a guest I wanted to hear.

On the price of drinks, I think it's largely a matter of "pot luck". The cheapest regular folk venue for beer I might get to is the Norwich pub that is hosting the weekly Irish sessions - his regular prices are very reasonable for the area. Possibly cheaper again depending on how you look at it is the Norwich Folk club - as far as I understand it they have no bar but welcome people bringing their own drink.

I think when one is looking for a venue, the main considerations are a suitable room for the occasion, a friendly environment and supportive management. If you are are lucky enough to have cheap drinks (or eg. it's not unknown for a session to offer one free drink for each participant), it may be considered a bonus.