Giving some indication on the globe where you are may bring some
exacting replies as to the cost and the best places, guess no matter
where you go you'll find some cheap, some reasonable and some
expensive....
... always get quotes from two or three places, I've dug this out for
you, it'll give you an idea of what's involved.
http://www.dnd.utwente.nl/~grit/backlight/ccft.html
May not be the backlight's it could be the dc-dc inverter that drive's
them, when the tubes go they usually either flicker or the 'white's in
the display becomes tinted, the inverter can give the same symptoms or
just go without warning.
davy