Debug interface: The STM32DISCOVERY kit uses Single Wire Debug interface to debug/program the microcontrollers.
Cost & Ordering: The STM32VLDISCOVERY board costs only around Rs 900/- and can be a very handy ARM based development tool for prototyping. In India you can order this tool from Kits-n-Spares /element14 website .
Prototyping: The STM32 family microcontrollers come with a wide range of package choices. For prototyping you can order a LQFP64 pin package chip and use the LQFP-64 break out boards available from NSK electronics as a base to solder the IC. Development environment: The STM32 family is supported by IAR systems and Keil. I prefer to use IAR emebedded work bench STM32-kick start edition which is free and provides a neat developing & debugging platform with Live watch and unlimited breakpoints features.
PS: The ST microelectronics has also launched other low cost discovery kits for its STM32F4 ARM Cortex-M4 microcontroller family.