Kalibri Labs recently published an in-depth special report at a critical component of the hotel business.
In a nutshell:
Cost of customer acquisition has risen dramatically over the last 5 years as the proportion of intermediated events has increased, equating to over $4B in costs and is expected to reach close to $8-10B by 2022. The total costs can reach upwards of 35% of room revenue per group when all costs are considered.
You can download and read the complete report here: Kalibri Labs