I have seen .com.ng and other top level Nigerian domains being sold online for up to $150 per year. I think the actual retail price should be about $25.

The main problem people have when registering these domains are:

1. DNS Issues - the secondary server MUST be in a physical location
quite separate from the primary, and that the two MUST be on completely
separate international backbone providers. (Most hosting facilities do not have this option)
2. Requirements for specific domains - RC Number required for .com.ng etc,

3. Administrative contact required in the company - email/phone/full name (company gets a phone call to confirm).
4. Company with a physical address in Nigeria

Items 1 can be sorted by either ordering a DNS service from http://darwindirect.net or by buying a hosting your intended .com.ng website there
Item 2 - make sure prequalify your clients in accordance with the list below:

Schools granting baccalauriat degrees <name>.edu.ng

Commercial <name>.com.ng

Governmental entities <name>.gov.ng

Not for profit organizations <name>.org.ng

Network infrastructure (i.e. isp routers) only <name>.net.ng