There are many methods for estimating size, effort, schedule and other cost aspects of IS projects, but only one specifically developed for Enterprise Resource Planning (ERP) [67] and none for simultaneous, interdependent ERP projects in a cross-organizational context. The objective of this paper is to sketch the problem domain of cross-organizational ERP cost estimation, to survey available solutions, and to propose a research program to improve those solutions. In it, we: (i) explain why knowledge in the cost estimation of cross-organizational ERP is fragmented, (ii) assess the need to integrate research perspectives, and (iii) propose research directions that an integrated view of estimating cross-organizational ERP project cost should include.