Say my app generates 1GB of logs per day. If I create a dashboard showing hits/errors for the last 24 hours and have the dashboard refreshing every 5 minutes it might cost me $1.44 per day (0.005 * 12 * 24).
By comparison list price for Sumo Logic is $90/month for 1GB/day of data (stored for 30 days) with queries being "free" (although there are limits to the number you can do).