Thank you! We put a lot of effort into maintaining quality documentation, so I appreciate the compliment!
Our pricing is intended to scale with an application. $1 per 1,000 API requests / mo is expensive for an application with thousands of requests per second, but I would imagine an application with that kind of traffic would fall into our enterprise tier which provides volume discounts. We also have a nice free tier for testing out the product in some capacity at any stage and offer better deals for early stage startups.
Regarding rate limiting. It hasn't really been an issue for us yet. As an API product, the only users I would rate limit would be free tier customers who are generating tons of requests and degrading performance for paying customers (hasn't happened yet). For paying customers, I would probably want to scale our infrastructure to support the amount of traffic they're bringing in since they're paying.