Pro is substantially more expensive than flash. In addition, there's wide variance in price with DeepSeek themselves providing the cheapest tokens last I checked (but they train on them). Caching policy also varies by provider. TTL can be as low as 5 minutes or as high as 24 hours and reading from the cache might or might not reset the timer. Whether or not you get a hit makes (IIRC) a 10x (edit: it's actually 50x) price difference in the case of DeepSeek themselves.