It is expensive! My DS visited 7 unis across 6 trips. Each trip required a drive of at least 2 hours or usually 3 or more, with one being visited by train which cost almost £300 for 3 of us, even with railcards.
For 3 visits stays in Premier Inn were needed, ranging from £50 to £100. The other 3 visits, we luckily had friends or family who lived nearby who put us up.
One of them was visited without an over night stay, but for most, with stuff starting at 9.30 or 10am, we found it was better to get there a bit earlier and being there the night before helped that.
Then there was food. The overnight stays required a meal out, and for lunches we had a mix of packed lunch bits and visits to cafes.
I never totalled it, but suspect we spent £1.5k or a bit more.
But that said, we tried to view the visits as mini weekends away and I will always remmeber that spring where we visited all those places and the world opened up to DS. It was amazing to visit the places and see what he thought and share the process with him. For me, it is one of the key events in his growing up that I will remmeber really fondly.
But without a doubt, you have to plan your calendar to fit the stuff in and get hold of accommodation and train tickets before prices rocket, and know it will cost. Of course, you can limit your number if visits or the geographical distance from home that you look at and these things will reduce the cost.