My advice is stop now.
Yes you can simulate a person doing web requests with the classes provided by c# but you will only ever be jumping on the boat after it has already sailed.
As bnt has already pointed out - your going to be at a disadvantage for a start in trying to screen scrape - you will find that it will be easy to do for the pure reason that when you screen scrape you will be scraping old news and at best you will be scraping values that have already been marked up by the vendor your scraping from.
If you are going to try and enter such a competitive market ( I suggest you dont because you are displaying a clear lack of understanding and key entry into the market) then you need to enter in before others have added their markup.
There is no money for old rope in adding more onto what is already a very slim margin as anyone searching the net will probably find your source - so it will be time ill invested.
If you really want to approach it in a serious manner then you need to negotiate to be on the same terms as the rest of the expedia's etc in this world. That is unless you can find a niche market they are not interested in.
I personally would say you should walk away unless you are doing one of two things - 1) Offering a clear cut service nobody else offers - or 2) offering it at a substantial cost saving. Seeing as the majority of ppl in the market place are trying to do both you really need an outstanding product to succeed - its not impossible - but not far from it.