It varies widely.
In most of the places I go, between $4 and $8. Just looked up the exchange rate: right now, equivalent to £6 to £12. Plus tip of about another dollar per drink.
That's for anything from American craft beer on the less expensive side to something like Delirium Tremens.
If you want something like Bud Light... I'd guess you could find them for $1 or $2 on special.