Do we get the source files?

What does "a lot" mean? 500 euros, 2000 euros?
Money can be raised. I'm sure that many forum members would support this initiative financially. Perhaps it would be worth creating a special fund for this purpose – to support modders. Any forum member, and not just forum members (there's also YouTube and social media), could contribute to the common cause by donating any amount they are willing to give.

I am almost 100% sure that the price was not named with the intention of making a profit, but rather as a way to gauge interest.
Based on the license under which the game is distributed, its source code cannot be distributed in any form. Therefore, since Quantomas is already an adult, or rather, a mature person, he is unlikely to violate the license agreement by giving the source code to someone, even for money.
Besides, even the amount of 5000€ is quite small in the realities of illegal intellectual property, and prices can be inflated for a long time, and I, despite my love for the game, am not ready to spend a lot of money, and considering how many people play Heroes, and how many of them will pay, the money may not be raised at all.
So, the source code can be said to be an unattainable thing.