Similar here - DS1 visited 8 (Oxford with school, then the others split between DH and myself accompanying, since one of us stayed at home with DD and DS2, who were too young to be left at the time). We swapped for offer holder days, so could each add our twoha'penceworth re all 5 that DS1 applied to.
DD did loads - a mixture of taster days, campus tours and proper open days - and all with yours truly, as I was more flexible re time than DH. It was fun, if tiring. And yes, quite expensive, with some overnight stays, but we worked it out. In the end, she chose the same university as DS1 (Birmingham); it did feel a bit like the story I remember from my early childhood, of the little old lady who decided she wanted to move house, so had an estate agent tour her round several houses and eventually found 'the one' - her own. But hey ho.
Poor DS2 (2021 entry) only got in two open days of his own, and no in-person offer holder days, but fortunately had come along with DD to a few universities and was quite familiar with Birmingham by then, so did have opinions about enough to make a choice re where to apply. Which did include Birmingham(!), but he chose to firm UEA, which is where he is.
At my insistence, we mainly travelled by train, as that is how they would mainly be travelling themselves.