Like many cities, bargains are few and far between on the main pedestrianised shopping streets, ie the Grafton Street and Henry Street areas. Street selling, along the lines of markets in Amsterdam, Paris or Berlin, is not so popular in Dublin, apart from excellent food markets at Moore Street and Camden Street, but there are still some bargains to be had. But check carefully, and beware of offers that seem that little bit too good.
From St. Stephen's Green, if you walk westerly to Camden Street or slightly further to Thomas Street and Francis Street, things are maybe not of designer quality but they are definitely less expensive.
Turn off Henry Street on to Liffey Street and good bargains are to be found on clothes and household goods. For good deals on hardware, outdoor and survival gear, and especially furniture, the best place to go is Capel Street (at the end of Henry Street, keep walking on past the Jervis centre through Mary Street and Mary's Lane).
For cheap luggage and haberdashery (great word that!), head for North Earl Street (across O'Connel Street at the other end of Henry Street)
Cheaper books, electrical equipment and music can be found on Crampton Quay and Aston Quay alongside the river.
Seasonal sales are held in most shops throughout Dublin's city centre in January and July. Designer stores on Grafton Street such as Brown Thomas and its designer sibling BT2 really do have real, honest to goodness bargains on the big designer names ... that is, if you are prepared for the mortal sin of being seen in last season's designer wear!