Depends where you go. I hire a lovely, good sized arena with a full course for £10/horse / hour. That's very cheap for the area. I've paid that for a 20x60 with no jumps before. Other places might be double that.
An indoor, I'd expect £30ish / hour with jumps / dressage boards.
Huge variation around me.
Private yards hiring out their arenas, I have paid between £6 and £20 ph
Show centres I have paid between £15 and £70 (yes!! ) ph. but mostly in the 25-30 range.
Huge variation - round here from £5/hour for a skanky surface 20 x 40 to £35 an hour for huge waxed surface with a full set of top notch jumps. That’s outdoors. Indoors have an extra premium