1. A system, comprising: a plurality of computing devices configured to implement a plurality of resources of a provider network, wherein the resources are organized into a plurality of resource pools, wherein each resource pool of the plurality of resource pools has an associated pricing policy and an associated resource usage interruptibility policy, and wherein at least one resource pool of the plurality of resource pools has a different resource usage interruptibility policy than another one of the plurality of resource pools; and one or more computing devices configured to implement a resource manager; wherein the resource manager is configured to: receive a task execution query comprising a specification of a task to be performed for a client using one or more resources of the plurality of resources, wherein the specification has an associated target deadline for completion of the task and an associated budget constraint for completion of the task; determine an interruptibility characteristic of at least a portion of the task, wherein the interruptibility characteristic describes a suitability of the at least a portion of the task for being interrupted; in response to receiving the task execution query and determining the interruptibility characteristic of the at least a portion of the task, generate an execution plan for the task, wherein the execution plan comprises using a resource of a selected resource pool to perform the at least a portion of the task, wherein the resource pool is selected from among the plurality of resource pools based at least in part on the associated pricing policy of the resource pool, the associated resource usage interruptibility policy of the resource pool, and the interruptibility characteristic of the at least a portion of the task; provide an indication of the execution plan to the client; and in response to a task implementation request from the client, schedule the at least a portion of the task using a particular resource from the selected resource pool.