For starters, don't pay for a particular bug. Start with a vulnerability disclosure program that simply establishes a process for receiving vulnerabilities from external finders without promise of a financial reward.
From there, start with a small private program on some of your more hardened attack surface. Our team can work with you to compare your chosen attack surface against our benchmark data for similar organizations with a goal of attracting an initial baseline of attention from the community before scaling up rewards as your attack surface hardens.
Monetary value will typically depend on how critical the bug is, the more severe the vulnerability, the more the reward. In our recent 2020 Hacker Powered Security Report, we discovered the average reward for all vulnerabilities of any severity was $979.