How to choose bar-end shifters for a given groupset?
You do need an indexed, Campagnolo shift set which is set up for the same number of gears that your bike has. 

Centaur is 10 speed Campag, if I remember correctly, so something like this:

Campag Record 10 speed bar end shifter

If you bike is 11 speed, then this, or similar:

11 speed Campag bar end shifter

Keep in mind that you will also need a new set of brake levers without shifters, and that most aero brake levers are set up for a bullhorn style handlebar. You may want to change that as well. 

You will, of course, lose the ability to shift from the hoods or drops. 

As for price, you should of thought of that before you bought Italian components to begin with. :)

Edit:

Must I use:


Shifters of the same brand as the rest of the groupset? (Shimano/Campagnolo/SRAM) YES, They generally use different spacing between gears (Campag/Shimano) or different cable pull ratios (Shimano/SRAM).
Shifters of the same product line as the rest of the groupset? (Dura Ace/Ultegra, Record/Centaur) No. You may mix component levels, if they match brand and index number.
Shifters of the same model year or generation as the rest of the groupset? Helpful, but with a few exceptions, not mandatory.
Shifters with the same number of indices? (10 speed, 9 speed, 8 speed) Yes. No options, unless your shifting is friction.
Indexed or friction-type shifters?
Indexed requires indexed. Friction can work with most things, unless it is designed for fewer gears. Spacing doesn't matter. 


Edit 2:

Also, for what it's worth, I can't find any Campag time trial shifters which are any group set other than Record in any of their online available catalogs. It is common to only produce 1 high end model of specialty items like that, so they may only have made Record models. Also Record 10 speed TT Shifters are discontinued, so if you really want a set, get them ordered while there are still some available.