Registring fee

[Olivier Pequin]

My Flynax marketplace works very well with hundreds of registered members.

I want listings to remain free but I have an issue with spammers : they create about 3 new accounts per day and it is a lot of work to delete their accounts and ads everyday.

I want listing to remain free for all users, but I would like to put a 10 euro fee to register now.
Doing so, my users will be able to post their ads for free like before, and I am sure 99% of spammers won't create new accounts if there is a 10 euro fee.
A legitimate new user will be happy to pay a one in a lifetime 10 euro fee if he can post as many free ads as he wants once registered.

But I don't find how to implement this. Any idea ?