Will it be an ‘Audio Bible’ only (where all the content is Scripture), or do I want to put other audio onto it like songs, drama, sermons, etc.?
Will the audio product be for small groups? Individual use? Or will it be used in communities where a significant group of people will want to gather round to listen and discuss (often the case in oral cultures)? Check the speaker output of your unit to assure you have either the power or the means to connect with auxiliary speakers.
Is the ability to charge by solar power important? Would people be happy charging by hand-crank? Are 12V car batteries available? There are some very creative and efficient solar charging systems available which can be utilized, not only for digital player charging, but for other uses in the community as well. It may be worth it to invest in one.
You may be in a context where people have access to computers and might want to replace Scripture content by their own music. Consider finding ways to distribute which locks data. Currently it is not easy to lock an SD card. Some audio recorders like Megavoice have data locking features.
COSTs and Repair
Consider shipping costs, import taxes, and any necessary accessories like solar panels, SD cards and chargers. Repair may be difficult for certain types of audio devices. Cell phones are cheaper to acquire and repair but data is less secure.