[inparen]

If X is cost/per user, Y is your profit margin, X+Y is usually offered.

But for 5000+ users, profit will be like Z = 5000+ * Y.

So question can be how much of Z, you can let go (assuming you want to market to future customers, using this account as reference/example).

Question is, are they actually going to onboard all 5000+ ? You don't want to run in losses, if you offer rates, below your operational cost. May be ask them to do pilot run with subset of user with same rate, how much pain they will cause? Then, you can decide accordingly.

That sound risky, but hey, that is what business is all about. risk/reward ratio? I am afraid, there is no definite answer.

Whatever is the domain/industry, do you have some baseline pricing to compete against ?