Bandwidth and Steepness Requirement for Voice Recording

One of my design involves recording of voice,with the best quality at the lowest cost.
Of course,there is a tradeoff between these appreciations.
1)NAND and NOR FLASH EEROMs for MP3 are now available in the gigabytes and mass produced at the #50nanometer scale.This enables inexpensive recording of tens of hours,whereas previous technologies involving 512Kbytes EPROMs ans RAMs enable only minutes of speech.I would like to know wether there could be a very inexpensive availability of large storage components with the optimum trade of between cost(below 1$ per 1K to 10K components)and facility of assembling

2)once again, vocoders, chips with integrated electret mike amplifier and so on are very common nowadays.Who is the largest supplier?

3)bandwidth requirement for intelligible voice quality may be less than 300bytes/second.Internet voice channel provides good quality at 1700bytes/second, MP3 at 3800 bytes/second.Suitable bandwidth could be 300 Hertz to 1700Hertz,with 5th to 8th order stopband to prevent aliasing,and too much steepness of the filter may increase the THD,as in class D amplifier.What are the best criteria for design?