Cost efficient design of embedded HW/SW systems that need to meet certain requirements is a complex task due to the huge number of possible solutions, the "design space". Design space exploration methods depend on the designers' input in terms of application description, target architecture, and cost estimates for implementation alternatives. Obtaining feasible pre-implementation cost estimates causes lots of effort since the designer does not have confident information before implementation on the target architecture, or even different target architectures, has been performed. In this paper we present a methodology suitable for automatic cost estimation of synchronous data flow (SDF) graphs. We propose to start from an executable SystemC-AMS SDF specification, and demonstrate its automatic transformation and implementation for cost estimation on heterogeneous HW/SW architectures. The presented methodology allows the estimation of both HW and SW implementation alternatives of each SDF node based on a quick synthesis approach. These cost estimates are fed to a mapping framework to obtain a static binding and schedule for the architectures under exploration. With the proposed methodology the designer does not have to perform full synthesis and implementation for design space exploration. This is demonstrated by a case study of a Bluetooth baseband unit considered for implementation on a Xilinx Virtex-5 FPGA.