I asked myself this all the time before I watched their bbc show, and they explained on it how they get sponsors from companies to fund each part of the trip, eg a clothing company sponsor (pay for) the dinner in exchange for all the girls wearing a dress from their brand to said dinner and tagging them on social media.
I guess it’s quite clever in a sense in order to break even on such a big trip but I’d panic incase someone pulled out and I was left to foot the bill