Besides content marketing, email marketing and throwing money at Google and Facebook
What works in one company may not work in the next (read: ). The suggestions you get here are only untested theories about what might work. You need to test these theories to see if they will work in your market.
If I were you, I would model different GTM strategies. Pick the best looking strategies based on the models. Validate the assumptions in the model with market experiments. Tune each model with this market validation data, and then pick the lowest CAC strategy.
I have a white paper on my website that describes this in more detail.
I know is sounds like a lot of tedious detail level work, and maybe even very therodical if you have never done it before, but is it the only way for a startup to get it right.
As @Steve said, it's not the model that solves the marketing issues, it's validating your strategy. If you first make a list of all your assumptions about customers, the market, the need, etc. and test each assumption individually, you will get a good sense of whether your head is even in the right space to sell your service. Once you understand more about your audience, you can take the next step to test strategies within that space.
First of all, it's a terrible time to be in the industry you named, so any results you get from validation attempts now will probably not remain true in the future. So, while you can play with a bunch of what-ifs today, I recommend you shelve this business idea until there is a travel market and travel in general resumes in a relaxed way.