Hello bad_taste,
I'd say somewhere between 0 and 20 euros.
I had my self-installed graphics card unlocked for 10 DM (which was in 2001, and due to the currency conversion of 2:1, it's now naturally 20 euros

), for the coffee machine's cash register... and it immediately didn't work!!!
A little side story:
I also wanted to have my flashing inspection light reset at the same time, but the

categorically refused (due to liability and blah, blah, blah...).
Of course, I didn't have a VAG-COM device or a compatible interface.
However, the circumstances described above led me to build my own interface and have VAG-COM unlocked.
I have no regrets!
Because, even though the GRA (Gearbox Release Assist) was correctly activated, it couldn't function because the same workshop, a few years prior, had repaired the clutch master cylinder free of charge and, crucially, had not properly reinstalled the clutch switch, which is mandatory for the TDI (Turbocharged Direct Injection) engine. The clutch was constantly 'engaged,' meaning the GRA couldn't function.
With VAG-COM, even a complete beginner could complete the entire process in just fifteen minutes.
If the workshop had charged me for investigating their own mistake, it would probably have been more expensive than just getting the unlock code.
Best regards,
K.O.