We are selling a single product (a solitary plan with no optional addons) whereby the per-user/per month cost is based on volume.  If a customer purchases 1-4 user licenses, the total cost is $199 per user/per month.  If the the customer purchases 5-9 user licenses, the total cost is $179 per user/per month. If the customer purchases 10-24 user licenses, the total cost is $159 per user/per month.  Finally, if the customer purchases 25 or more user licenses, the total cost is $139 per user/per month.  This total per user/per month cost is easily calculated by us but I have found no way to implement this using Zoho's built-in functionality.  The formula is basically a core price of $199 with an approximate 10% discount applied for each of the four volume tiers indicated.

The bottom line is this.  I want the customer to simply supply their customer details along with their desired quantity and the Zoho form to magically display the final price on it PCI-compliant form.  How I do this is a mystery to me.  If someone knows how to implement the simple model described above using Zoho's built-in functionality, please enlighten me.  If ultimately it requires some combination of my own custom HTML forms and code, combined with leveraging the Zoho API to supply the resultant per user/month cost to Zoho, that's fine too.

Assuming what I'm trying to do is possible (one way or another), I would also like to enable the customer to be able to purchase 'n' additional licenses later and recalculate their total monthly cost going forward based on the new aggregate quantity.  Case in point: If a customer purchases 15 user licenses of our product, they would be presented with a recurring monthly bill of $2385 (15 users x $159/per user/per month).  Later, if they opt to increase the number of users to 30 users, their monthly bill would change, going forward, to $4170 (30 users x $139/per user/month).  To do this, I assume that I would need to know that the customer is an existing customer and then, using the API, look up their existing info, calculate their new total user quantity, and subsequently recalculate their new total recurring monthly cost based on that new quantity.

Thanks in advance for any-and-all assistance.