During most of my time there I didn’t have a phone,
I can't even fathom how one survives without a phone in Chinese cities. At least nowadays, it's a literal requirement. You ain't eating or travelling if you don't have a phone connected to the internet.
cost me about $80 USD a month
That's wild lol but I can absolutely believe it. I think even when I first moved to Shanghai, a decent apartment was about 3,000rmb. The same place will be going for about 15,000 now.
Honestly though my time in Xiamen I was... unimpressed. My literal only memory of it is just how much construction was everywhere. The first beach I saw was completely ruined by the fact there was about 7 elevated highways dominating the view above, with the pillars crashing through the sand turning it downright dystopian. But yeah, I can envision the good times. Sad!