Do you have confirmation the injector(s) are bad? I rarely see GM fuel injectors go bad, sometimes they can get stuck closed if they've been sitting in old fuel for years. Not a problem on a daily.
If you have a misfire, start with the basics: air, fuel, spark. Focus on fuel/spark for the 1.4t for now.
The OEM coil pack on the 1.4T is known to be weak, pull it off and make sure the boots aren't corroded or broken. Check your spark plug gap, coupled with the weak factory coil and a turbo, we can get spark blow-out which causes a misfire. Regap them to 0.28. Refer to this thread for more info:
http://www.sonicownersforum.com/forum/1-4l-turbo-sonic-engine-discussion/4118-spark-plug-gap-6.html
If you have a misfire code, try swapping the fuel injector between cylinders to see if the code follows the injector. It's pretty straightforward to pull the fuel rail off these cars, it's right on top near the firewall.
Hate to see you throwing $$ at injectors when they may not be the problem, if some basic diagnostics show they're bad, then go for it!