You can easily do your own tube feeding, and the vet could sell you the kit for very little. My vet sold me a tube and catheter for $3. Or you can get tubing from Walmart or an aquarium store. Drug stores will often give you a syringe for free. Be sure it will fit in the tubing.
There are tutorials on tube feeding here on this site. Here is a photo to show you where the syringe or tube needs to go to do this safely. It's much easier than you would think, and you'll be better prepared in future to care for sick chickens confidently.
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