Update Pricing information for EIS endpoints (#3112)

Update pricing information for ELSER and ELLM

Co-authored-by: István Zoltán Szabó <szabosteve@gmail.com>

Author: shubhaat

explore-analyze/elastic-inference/eis.md

@@ -61,3 +61,7 @@ This is particularly relevant when using the [_bulk API](https://www.elastic.co/
 #### Rate Limits 
 
 Rate limit for search and ingest is currently at 2000 requests per minute.
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+## Pricing 
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+All models on EIS incur a charge per million tokens. The pricing details are at our [Pricing page](https://www.elastic.co/pricing/serverless-search) for the Elastic Managed LLM and ELSER.