I absolutely love this idea. Do it. Ignore the grumpies suggesting objectification or privilege. It's a market for attention. Nothing more, nothing less.
A woman getting dozens of low-effort messages knows that the next message she receives could be from her next amazing relationship. Great people are less common than low-quality pussy-beggars. That's just life.
Charging for messages just optimizes for the sort of loser desesperados who are even open to the idea. It really is just a sugardaddy-finder.