Go into your steam library, not the achievments page.
Hover over the Shopaholic achievment you should see a negative number:

Write that number down.
This negative number must now be converted into an unsigned 32 bit integer.

For example use this website https://www.online-python.com/
And enter

And replace <your number> with the negative number you have found.

Run the code and now you can see something like:
at the bottom.

Copy that number in the paranthesis.

Download a memory manipulating programm like: https://cheatengine.org/

Start a new game and pause it.
WIth CheatEngine select the game's .exe

On the right do a new search 4 Bytes, exact value and enter the value you gotten via the first step.

Now only one value should appear on the left.

If you see multiple values, spend 500 gold and end the turn. One of the numbers now should have been decreased by 500 pick that one. Note: These number are updated at the end of a wave!

Set this value to 50000 (Maybe something bigger 50000 works too). Don't spend any gold, else the value decreases. Now just loose the game. And you should get the achievment.