According to a report from Varety, Warner Bros has spent around $25 million so far on reshoots for the film. Also currently causing problems for some of the cast in terms of their own filming schedules since its been going on for the past 2 months.
One big reason is due to the new director wanting to flesh out more of the stuff Synder filmed so the scenes link or fit better together.
In terms of comparisons, a normal reshoot process is usually just 1-2 weeks and between $6-$10 million at most.
http://variety.com/2017/film/news/ju...ts-1202502433/