Here's a recent (2012), and excellent, analysis and estimate of the development costs of a new medicine (specifically an NME, a chemically distinct, novel molecule). There is a good overview of the historical trends in costs and attrition, and a collection of all significant previous estimates of the R&D costs of a new drug. There's some nice exploration of the sensitivity of the costs to various factors, and differential success and costs across various therapeutic areas.
In case you wanted to jump to the punchline, the costs in this study is $1,506,000,000 (i.e. $1.5bn) at 2011 USD prices.
The report is free, with only registration at the OHE website required to download the report. Great value!
%T The R&D Cost of a New Medicine %A J. Mestre-Ferrandiz %A J. Sussex %A A. Towse %I Office of Health Economics %D 2012 %O ISBN 978-1-899040-19-3