The issue that you're having with your own pipeline is that you don't realize that the output from grep is several lines long, with one integer on each line. The numbers are outputted on the same line only because you use $price unquoted.
If you want the average price, i.e. the amount after the avg: tag, then it would be easiest with awk:
curl -s 'https://...
I was using curl 7.60, built from source. After upgrading to the newest version it started working again.
Using fedora 32, because dnf depends on curl, I had to use rpm to remove and upgrade the packages.