I would have to find a way to get 100 at 5 Euros each plus any shipping.
That's already stretching it. I won't be asking for money up front.
If someone else with deeper pockets that wants a majority of the pieces wants to do the buy then I would hope to buy from them.
Looking on the web just now I see 5 Euros is US$6.42. I think that it packs a lot for that price.
Arduino will run 8 MHz on 3.6V won't it? I'd also be looking at if these things can simply be hooked up to button circuits as stand-alone.
I think that a guy like you would also be interested in a book like this:
http://www.vsdsp-forum.com/phpbb/viewtopic.php?f=11&t=36
The book compiles together a lot of information, which otherwise would be difficult to piece together from different sources, such as datasheets, application notes and C header files. For example, it tells how to use all of the 22 input and/or output pins of the VS1053. The book explains the structure of the VS1053 audio path and teaches how to write VSDSP interrupt handlers in both assembly and C language. All of the examples use VSIDE, with step by step guide on how to obtain, install and use the graphical development environment.
In my current ongoing state it would put me to sleep but maybe some day again I could use the like of it.