Hi, I have a digital marketing practice in India. Since 2008, with my team, I have helped businesses across industries and nations grow sales through online media.
Addressing your query, this can be done in a number of ways. One of the bests ways is to:
For Facebook: As per your audience profile and target locations, you can get approximate cost per reach, cost per conversion in Facebook Ads. This will help you set you daily budgets.
For Twitter: You can get Promoted Tweets done at very competitive budgets.
For Google SEO: This will require sustained efforts and a long term strategy. As above, narrow down on your target audience profile and target locations. Research on their online behavior, for this, you can analyze competitors' websites, their traffic patterns, keywords and get yourself a keyword research done. Based on results, optimize your website such that it addresses needs of your target audiences. Start blogging on relevant topics and build your brand's online reputation, visibility and ranking. Voila, you will see your website start ranking on top SERPs in few months time!
For SEM: Above research will help you get estimates for cost per click, cost per action, as per your objectives; from Google Adwords. You can also explore Bing Ads if that works.
For Travel Portals, you can contact them directly and get quotes.
I hope this addresses some of your queries. All said and done, it is IMPORTANT that you have a CONVERSION STRATEGY in place. I can say this from experience wherein many businesses have awesome websites but abysmal sales conversions. Many of my clients from the hospitality industry had this issue, wherein my first step was to improve their Traffic Conversion ratio.
Feel free to contact me if you have any further queries or would like to brainstorm on ideas.