any advice please :(

You are in a very tough and highly competitive marketplace with competitors who would think nothing of spending 7 figure sums on internat marketing a month globally.

Without knowing specifics it is impossible for your questions to be answered. However your best best is to go to established internet marketing companies and invite a tender. Lay out in the invitation what you are hoping to achieve and shortlist the replies. Check references and make your choice.

Only those companies who understand what you want to do can really give you advice on how to do it.

I agree with “mademetop” that you are in a very competitive niche and to outrank the other competitors in your target market, you need to search for a recognized Internet Marketing service provider and hand over this to them.

But without knowing objectives of your Internet Marketing Campaign noone would be able to provide the answer on how much would you need to spend and how much time would it take?

do you really want to compete with the big ones? as stated above, they have big monetary resources and are big spenders when it comes to advertise.
Why not start by promoting a special niche and grow from there?

I know it is probably not the answer you wanted, but this is the way I go when facing fierce competition.

Booking.com and Hotels.com are major spenders, and have a huge hold in this marketplace. Suggest not competing with them period, you'll get crushed to bits trying to compete.

Maybe there's a Travel booking niche you could do instead.....

In this world there will be too many competitor of any products or business. Please don't be afraid. You should start SEO work for your site first then you can post classified ads to various sites.