If using GNU awk, try this. Adds the commas by making use of the ' modifier.

$ awk '{sum+=$1}END{printf "%'\''.2f\n",sum/NR}' <filename
1,316,375.05
$

From gnu.org : gawk Format Modifiers

A single quote or apostrophe character is a POSIX extension to ISO C. It indicates that the integer part of a floating-point value, or the entire part of an integer decimal value, should have a thousands-separator character in it. This only works in locales that support such characters. For example:

If using GNU awk, try this. Adds the commas by making use of the ' modifier.

$ awk '{sum+=$1}END{printf "%'\''.2f\n",sum/NR}' filename
1,316,375.05
$

If you've got jq, try this.

$ jq -s min,max,add/length filename
1153022
1439480
1316375.05
$

From gnu.org : gawk Format Modifiers

A single quote or apostrophe character is a POSIX extension to ISO C. It indicates that the integer part of a floating-point value, or the entire part of an integer decimal value, should have a thousands-separator character in it. This only works in locales that support such characters. For example: