In mobile ad-hoc peer-to-peer (M-P2P) networks, data availability is typically low due to rampant free-riding, frequent network partitioning and mobile resource constraints. Rare data items are those, which get sudden bursts in accesses based on events as they are only hosted by a few peers in comparison to the network size. Thus, they may not be available within few hops of query-issuing peers. This work proposes E-Rare, a novel economic incentive model for improving rare data availability by means of licensing-based replication in M-P2P networks. In E-Rare, each data item is associated with four types of prices (in virtual currency), which provide different rights to the query-issuer concerning the usage of the item. E-Rare requires a query-issuer to pay one of these prices for its queried data item to the query-serving peer, thereby effectively increasing data availability and combating free-riders. The main contributions of this paper are three-fold. First, it provides incentives for replication of rare data items by means of a novel licensing mechanism, thereby improving rare data availability. Second, it provides additional incentives for MPs to collaborate in groups, thereby further improving rare data availability. Third, a detailed performance evaluation has been done to show the improvement in query response times and availability of rare data items in M-P2P networks.