Yeah, I was looking at custom coded website. It would cost from $1500-2500
The thing with booking.com is they expect you to host all their files in your own database if you want to use your own custom configuration with their xml feed. This also includes the images which total about 70Gb. Combine this with daily changes, deletions, additions, etc and it's not a 2 minute job - and that's just maintaining the data. I set up a system allowing people to create sites using my databases along with their own booking.com affiliate id but it generated little interest. Perhaps look at their white label options although you are then limited on how the search engines will see your site.