Zoho Payment Gateway Plugin Development

we would like to develop a payment gateway plugin for Zoho. Using our payment gateway API's
Considering:
- security
- support all payment gateway API fields
- support all payment gateway callback fields
- configuration options in the admin control panel
- use the latest PHP functions (without deprecated functions)
- use best practice PHP functions instead of normal functions
- support multi-currency

We expect the developer to be within the original and agreed on budget.