A study published by Steve Paul et al.

A study published by Steve Paul et al. in 2010 in Nature Reviews: Drug Discovery compares many of the studies, provides both capitalized and out-of-pocket costs for each, and lays out the assumptions each makes: see Supplemental Box 2. The authors offer their own estimate of the capitalized cost as being ~$1.8B, with out-of-pocket costs of ~$870M.