Depends on your preference and what you define as cost effective.
Almost certainly you would need to replace the front and rear mech along with the brake levers.
Possibly the best way to do this is to buy a groupset.
If you are not stuck in the "must be Shimano (or Campag)" camp then a set of levers, front and rear mech can be got for around £120 (Microshift), but if you are in that camp then, for new, you are looking at £300 for Tiagra then working your way up through the groupsets, 105, Ultegra and DuraAce (unless you are lucky and find someone with a groupset going cheap, on here or elsewhere).
You *may* have to replace the rear wheel, and don't forget you will need downtube cable stops (another £10).
As time has gone the main players (Shimano and Campag) have sought to get people more and more locked into their groupsets. At one time there was a number of different manufacturers kit that played nicely with other people's kit, not now. There are even compatibility issues between stuff fromt he same manufacturer (Shimano front road mechs won't work with MTB levers, Ultegra 6700 and DA 7900/9000 levers won't work with 6600 or 7800 to give just two examples).
