There is no way to easily measure the ROI of everything.
Especially not in the advertising world.
Management often wants proof that for every dollar they spend, they're going to get three, four or five dollars back. This can drive you to use the same advertising channels exclusively, because they lend themselves to measurement, if not marketing effectiveness.
But those channels best suited for measurement are also the ones best suited for direct transactions (spelled p-r-i-c-e), not brand-building (which is what will drive rate). And that measurable ROI is usually going to be fairly low if you're selling on p-r-i-c-e. It also assumes that the last touch was exclusively responsible for the purchase decision. Which is almost never the case.
Think about full path attribution (and you should). This includes everything that affects that decision to book – the commercial they heard that made them more receptive to the ad they saw that nudged them to click through the Google listing they saw to the website where they actually reserveda room.
A smart independent hotel will move away from spending as little as possible on low-cost digital channels and think more about spending on an overall effort. An integrated family of tools. Don't base your media decision solely on what is the least expensive. After all, if the only thing that counts is the cost, then doing nothing at all is free, isn't it?
Besides, how did you calculate the ROI of whatever that recent renovation cost you?