How to insert $ before a string with regular expression in VScode?

With this regular expression

VSCode could replace

# W1 blaAAA
# W2 blaBBB
# W3 blaCCC

with

# W1$ blaAAA
# W2$ blaBBB
# W3$ blaCCC

namely, appending a "$" at the end of W\d{1,2}.

Now, I am trying to insert "$" before W\d{1,2},

for example, replace "W1" with "$W1", I tried $$1 and \$$1, none of them worked.

Any clue?