There is a very cheap alternative to MBED LCP11U24: ST Discovery F0 development kit. The board is available at an amazing price which is almost 1/8 of the CORTEX M0 MBED one and almost 1/3 of Arduino Uno price. Discovery is not so easy to use as MBED or Arduino boards but is a very powerful tool to develop 32 BIT code based systems.
You can find more information here: http://www.element14.com/community/roadTestReviews/1347