Hi,
I am an Electronics and computer science engineer, I have experience working with various prototyping boards, Raspberry Pi, Arduino, mbed (ARM proto board)... as well as developing custom PCBs, you can find some of my projects on my portfolio.
The price and time frame suggested here is simply a placeholder, as I didn't quite understand what you mean by four of these, is it four different projects with different requirements?
Also, the widely used microprocessor for this type of applications (and for a good reason) is ARM, which I advise you to use for many reasons.?
Last question before we discuss this in detail over chat/phone: can you describe the functionality in terms of user stories, ie imagine that you have the product in your hands, describe using the different functionalities, for ex:
_ As a user, I'd like to be able to record an audio stream and send it to my phone.
I pride myself on ensuring that the customer is satisfied with the quality of the work and strive to sustain good communication and complete the project (5-star reviews/ 100% completion rate)
Looking forward to working with you.
Regards,
Nabil