adding bullhorn handlebars, what about shifter and rear derailleur? I am changing to bullhorn handlebars and I'm having some difficulty figuring out what sort of derailleur and shifter I should get. I would like to use a 9 speed bar end shifter as I currently have a SRAM X5 1x9 drivetrain running 11-34 - 9 speed cassette with a 42T chainring.

I will be mostly commuting and I don't want 'bottom of the barrel' as far as price but I also don't want 'top of the line' professional components either.
We don't do product rec here, but I will note that SRAM rear derailleurs are compatible across road and mountain groups for 9 speed, as are Shimano. 

So, if you have a Shimano rear derailleur, buy another Shimano shifter and keep the existing derailleur (or Shimano compatible, e.g. from Microshift). If you have a SRAM rear derailleur, replace Shimano with SRAM in the last sentence and ignore the parenthesis.