The article presents a detailed index of usage-based pricing models for various AI services, focusing on leading providers. Each entry includes specific pricing models, packaging options, and credit systems. For instance, Grok AI offers a hybrid model with freemium and tiered subscriptions, while its API provides token-based pricing starting at $30 for business users, scaling to custom rates for enterprises. Notable entries include an AI art generator using multiple models, which operates on a tiered usage model with promotional credits. Another service combines real-time web search with large language models for structured responses, utilizing a prepaid credit system. OpenAI's offerings are highlighted, with their developer platform relying on usage-based pricing and prepaid credits, while their flagship conversational AI features a flexible subscription model. Other diverse tools are listed, such as a meeting transcription service with hybrid pricing based on seats and usage caps. An AI-powered document analysis platform caters to corporate teams with custom enterprise pricing and a focus on querying large unstructured datasets. Each model reflects the trend of flexibility in access and payment, accommodating different user needs from casual consumers to large enterprises.