Then I heartily recommend the second-hand bookshop attached to Whitefriar Street Carmelite Church.
You can find some wonderful Catholic and Christian books there (not to mention some fine secular titles), most of them very cheap indeed. Today I bought To Be a Pilgrim by the late Cardinal Basil Hume, for one euro. On previous visits, I've found Chesterton's biography of St. Francis of Assisi and some other good stuff. There are many old, handsome hardbacks-- I remember a rather splendid, two-volume biography of Cardinal Manning, that I persuaded myself I didn't really want or need.
They also have a "to clear" trolley outside where everything is going for ten cents. I've picked up past issues of various Catholic publications there in the past. The reading of old periodicals is a unique and rather contemplative pleasure, one that Orwell lauded in one of his less bellicose newspaper articles. (Unfortunately, on today's visit I found little on the trolley besides old copies of The Tablet-- I'd read about The Tablet's reputation before, but one look at the names of its contributors and the titles of its articles convinced me it was better left unread. I think I would rather read Jack Chick than John Cornwell.)
Old magazines, if you can find them on sale, aren't always especially cheap. I recently acquired several old copies of Studies from the bargain stand outside UCD's Campus Bookshop, at a euro each, but the old periodicals to be found in Chapter's bookshop in Parnell Street are no cheaper than their second-hand books-- which aren't very cheap themselves.
To me, a bookshop isn't a proper bookshop if it doesn't yield surprises, if there is no potential for a happy discovery. Also, it needs to have a character and a soul-- that mysterious tendency to throw up books of a certain type or period, often cutting across boundaries of genre and subject. (The Books Upstairs in the Omni, now closed, had a particular penchant for disasters and the occult, for instance.)
What discoveries are to be made on the shelves of Hughes and Hughes or Hodges Figgis or Dubray Books, except a perfect reflection of the latest intellectual and literary fashions, the TV schedules and the multiplexes? They are utterly impersonal and soulless-- the handwritten book recommendations by members of staff that are tacked to some shelves are a forlorn attempt to make them seem less impersonal, but the recommendations are so utterly predictable as to totally belie this. Doubtless, like everything else, selling books is becoming more of a science all the time, and less and less room is left over for serendipity or happenstance. How much we sacrifice on the altar of Efficiency!