I am trying to get this formula to ignore the times on the data in column D and look up the date to calculate the costs per day, but can't seem to get this working.
I don't know why you are apparently trying to sum B:B from B2; that seems like a circular reference. I believe you are trying to sum E:E.
=sumifs(E:E, D:D, ">="&A2, D:D, "<"&A2+1)