Your choice depends on the complexity of the DSP algorithms in your application. The more complex the DSP algorithms, the more practical using a DSP chip.
If you can elaborate on your projects tasks, I maybe able to make a recommendation as to a specific platform.
By the way, a third option would be a FPGA, where you can combine a softcore cpu and custom dsp blocks all implemented in the FPGA.
FPGA Dev Boards range in price from $100 to several $1000 depending on the project requirements.
A good starter FPGA board:
An interesting STM32/MATLAB Simulink Combo:
FiO-Std with RapidSTM32
DSP chip based dev board tend to be in the higher range, as you well know. Choosing an appropriate DSP based board is very dependent on its application.
As I previously mentioned, if you can be more specific on your intend projects task, a more definitive recommendation can be made.
BigDog