I'm in same wagon like you, trying to select an smartphone with WIFI and available SDK, low cost (lower thatn 40$). Also contacted Mediatek without results. I can give you a piece of advice, in reality is what I'm doing now. Try to negotiate a bulk purchase with a supplier together with access to SDK and documentation. I did that before with an ARM based Thinclient and worked, but I had to buy 30 pcs.
