In practical settings of wireless sensor networks, it is often feasible to consider heterogeneous deployments of devices with different capabilities. Under prescribed cost constraints, we analyze such heterogenous deployments and present how they impact the coverage of a sensor network including spatial correlation effect. We derive expressions for the heterogeneous mixture of devices that maximizes the lifetime coverage in both single-hop direct and multi-hop communication models. Our results show that using an optimal mixture of many inexpensive low-capability devices and some expensive high-capability devices can significantly extend the duration of a network's sensing performance, especially in a network with low spatial correlation.