I lived in a Tier 3 city from 2015-2016, teaching at a public high school through AYC. The cost of living in a city like mine is incredibly low. Living within your means is more than possible.
My city was incredibly affordable. Through AYC, you'll be living in paid housing, which means no rent to pay, no utility bills, and free wifi. Many schools also provide free or discounted lunch for their teachers during the school week; my school's buffet (yes, BUFFET) lunch was Y6 each day ( or about 90 cents). And that's not the only way AYC placement schools are different than other programs'. The public bus system is convenient, with the cheap price of only Y1 to board.
You'll burn through your money fast if you eat lots of Western food or drink Starbucks coffee. Just one coffee will cost anywhere between Y32-48. I did pretty well by purchasing a coffee pot for my apartment, and eating out with my Chinese colleagues or trying local food and street food. In Tier 3 cities, it's easy to eat a good dinner for anywhere between Y15-30. Cities are littered with small, fresh fruit and vegetable stands; I made a habit of stopping by one and getting Y2 bananas most days. It was easy to point to what I wanted, or translate the word on Pleco, a smartphone translation app. Western food can cost around Y50-80 per meal, so it was nice for me to splurge on that once a month or so. If you like going out, there's often deals and discounts; without these, going out was still pretty affordable. I generally paid Y30 per mixed drink, and around Y10 for a beer.
I didn't have any debt, but many of my friends had no problems getting money from their Chinese account to their western one through PayPal, and paying bills that way. You can read more about how to send money home here. They still had money to travel, buy winter clothes, and explore the city together as a group of EAs. I'll also add that traveling by bullet train is pretty great in China, and Shanghai is about an hour away, it costs Y79 for a one-way ticket. Changzhou is also situated near some pretty cool cities that are around 30-45 minutes away by train, like Hangzhou, Suzhou, and Wuxi (Wuxi is 15 minutes away, and you can check the availability and prices of tickets on Ctrip.) It's a great app to download on your phone, along with a few others. If you want to read more about the cost of travel in China, read this blog.
One thing I also did in the city was work a few Saturdays at an English training center, privately tutor coworker's children, and host a few public English Corners. These "side gigs" paid really well, and helped me save some money for bigger trips. I had two friends that took on several steady side jobs, and they ended up DOUBLING their monthly salary.
For me, I really treasured my weekends and free time, so I generally ate lots of Chinese food, took the bus or biked if I wanted to go around the city (instead of a taxi), and was able to live very comfortably within my means.