~snip
The cheapest subscription in Nigeria is to go for yearly plan and not *121# which can double the data for you for monthly subscription but still costly than yearly subscription. Annual subscription is still cheaper. Also the *121# offer is removed at anytime by MTN which makes it not reliable.
I didn't keep up with the data consumed because I had already accepted that it was going to consume more than I had planned/expected. From my rough calculations, the monthly plan is quite similar to the smart bundle, but just like you've said, it is not always available to every user at the same rate, and the plan changes everything. So, you can get a subscription for as low as N5K today and get that same plan for N7K the following day, which is not efficient at all.
Maybe you will be the first Nigeria that will be seen here -->
https://bitnodes.io/. Or maybe you are going to use Tor.
The link you shared looks interesting, but my software is already a few hours behind the current one, and my network is not even helping matters because it doesn't work during the day. I will try to get the complete block tonight and check the same link to see if there is any further update. It seems they've got their own rough estimate of Nigerians that have attempted running a node, but the key point is those that have a node that can relay information to other nodes.