Look at the $99 ---> $129 boards from Cygnal (Now Silicon Laboratories) that come with an expanded copy of the Keil Evaluation Kit. It includes IDE, simulator, full assembler and linker plus C compiler for smaller programs (but twice as big as the Keil eval version you download off the web). See here for some ideas on how the prototyping works out...

http://www.8052.com/users/mkaras/CygnalEval.phtml

Michael Karas