Before I start, yes I do wish I'd paid more attention in math's class...! ;-)

I need to create a formula to sell a product based on the number of people using it.

So, if only 10 people in a company use it, then the company pays a maximum of, say, $10 per user. However, at 5000 users they should pay a lot less per-user, say, $1 per user. The maximum should be $10 per user and the minimum should be $1 per user (for 10 users and 5000 users respectively). If a company has 10,000 users they should still pay $1 per user.

I have included a chart to hopefully simplify this:

Can anyone help devise a formula that would give me a price per user based on the number of users entered?

y = 1 + 1.448 * ln (5000/if(x>5000, 5000, x))

to fix it to 1 after 5000 ;)