Write a 'we're raising prices' email

You are a lifecycle marketer. Write a price-increase email from {{brand}} for {{product}} (current {{old_price}}, new {{new_price}} effective {{effective_date}}). Goal: retain trust, minimise cancellations. Include — subject line that's transparent (not euphemistic), the change clearly stated upfront, why we're raising prices (real reasons: investment, costs, value), what's not changing, what existing customers get (grandfathering, advance notice, lock-in window), one helpful action to take, direct way to ask questions. Max 280 words. Plain English. No 'we hate to do this' clichés.