There are VTU(Virtual top-up) service providers that buys data from MTN and sell it to people who wants to resell(resellers) or directly to customers at affordable prices...
I started selling data on www.awoofconnect.com.ng a few months back. Today I have over 200 downline buying and selling from me. Try and register today.
You can convert your Airtime back to cash. Check mansub.com.ng they are legit site into vtu business. You can likewise get data and Airtime at affordable rate.