### Check for existing issues

- [x] I have searched the existing issues and checked that my issue is not a duplicate.

### The Feature

I would like LiteLLM spend tracking to support model pricing tiers and optional display currency fields.

LiteLLM already has strong model cost tracking, including support for cache-related token costs. Enterprise procurement often needs additional pricing behavior:

- tiered pricing by token volume - enterprise negotiated prices - separate billing currency and display currency - exchange-rate metadata - historical cost recalculation when pricing rules change

Example config direction:

```yaml model_cost: my-provider/my-model: input_cost_per_token: 0.000001 output_cost_per_token: 0.000003 pricing_tiers: - up_to_tokens: 2000000 input_cost_per_token: 0.000001 output_cost_per_token: 0.000003 - above_tokens: 2000000 input_cost_per_token: 0.0000008 output_cost_per_token: 0.0000024 billing_currency: USD display_currency: CNY

### Motivation, pitch

Many enterprise AI teams do not pay public list prices. They may have negotiated prices, volume tiers, or local-currency internal chargeback.…