[Feature Request] Pay-as-you-go Billing model

### What problem are you trying to solve?

I don't know if this is the right place to discuss this. Feel free to close this ticket if I should be discussing this someplace else.

I'm a big fan of Deno and would love to migrate my pet projects from AWS due to its simplicity. However, the $20 monthly fee for the Pro plan feels a bit steep for these smaller-scale projects.

If my project reaches 1,000,001 API requests, the additional request would be dropped in the free tier. To accommodate even one more request, I would have to upgrade to the Pro plan.

### Describe the solution you'd like

I understand that this is a premium service offering a simplified DevOps API, and I respect that. I'm willing to pay a premium for this service because it's worth it. However, a fixed monthly fee of 20$ might be excessive for many projects.

Consider adding a new plan: `Pay as you go`. In this plan, you could charge more for specific types of services. For example, increase the cost per million API requests from $2 to $3 or $4, potentially exceeding the Pro plan's price. This way, developers only pay for the services they actually use. This could attract more hobby programmers to Deno Deploy, potentially increasing your sales.

You can continue to offer the Pro plan. As projects mature and developers utilize more of your services, they might realize that the Pro plan becomes more cost-effective than the pay-as-you-go model and are more likely to switch to the Pro plan.

### Describe alternatives you've considered

Not applicable.

### Documentation, Adoption, Migration Strategy

_No response_