It can be an idea to generate money by placing billboards on the parcours.
That way you can keep the user fee at a minimum.
As long as the graphics aren’t easy to overwrite locally. OK, most people won’t bother perhaps, but I can envisage ad strippers being implemented to replace in-game hoardings with blank or alternative graphics. Would need some sort of CRC/checksum on the game files when starting up to discourage people from doing that.