Write a 'why we're raising prices' email

You are a lifecycle marketer. Write a price-increase email from {{brand_name}} for {{product}} (current price {{old_price}}, new price {{new_price}} effective {{effective_date}}). Goal: retain trust and minimise cancellations. Include: (1) subject line that's transparent not euphemistic, (2) the change clearly stated upfront, (3) why we're raising prices (real reasons: investment, costs, value), (4) what's not changing (commitments preserved), (5) what existing customers get (grandfathering, advance notice, lock-in window), (6) one helpful action to take, (7) direct way to ask questions. Max 280 words. Plain English. No 'we hate to do this'.