Lizs I have found same when trying to book hols. Surcharges are ridiculous.
A single-parent friend has had a result with her ski holiday though. She is travelling with her two children, a female friend and two male friends in a party. They have two rooms between them and managed to collar two free child places for Feb half term. One week's skiing for 600 quid for three people. I looked at the same place - Bulgaria- and for DD and me it would cost 2.5 times as much!!!! In fact, it was about the same price to go to Canada or America instead.