You just have to quote them:
echo "\"$1\",\"$2\",\"$3\",\"$4\""
As noted here:
Enclosing characters in double quotes (‘"’) preserves the literal
value of all characters within the quotes, with the exception of ‘$’,
‘`’, ‘\’, and, when history expansion is enabled, ‘!’. The characters
‘$’ and ‘`’ retain their special meaning within double quotes (see
Shell Expansions). The backslash retains its special meaning only when
followed by one of the following characters: ‘$’, ‘`’, ‘"’, ‘\’, or
newline. Within double quotes, backslashes that are followed by one of
these characters are removed. Backslashes preceding characters without
a special meaning are left unmodified. A double quote may be quoted
within double quotes by preceding it with a backslash. If enabled,
history expansion will be performed unless an ‘!’ appearing in double
quotes is escaped using a backslash. The backslash preceding the ‘!’
is not removed.
The special parameters ‘*’ and ‘@’ have special meaning when in double
quotes (see Shell Parameter Expansion).