have you had the car setup correctly since buying it, or did you assume that it was setup correctly from the people you purchased it from?
its a pretty big job - a cam's out jobbie to replace the lifters, so id be looking to take it to a VW specialist - not a dealer to get it done. as u really want somebody who knows the 16v lump inside out to be fitting them & then getting it up & running correctly
if you where getting the lifters done, id get timing belt, tensioner, timing chain all changed at the same time - u may aswell do it all now cause sooner or later it'll need done. parts total for the above is about £170 then it just depends on the labour - id ring around a few VW specialists and get prices. tell them you'll provide the parts
i doubt you'll get the lifters fitted under warranty as they are a general wear n tear iteam. u could always try!!
i had my lifters etc all replaced there just at easter and the difference it made to the engine was unreal, the engine really is super smooth now at idle, not a rattle out of it anywhere