Just like GentleAndrew siad,IOM Nigeria will always get the best price reduction in flight cost for applicant.
I'm privileged to have a friend working there....so I'm going to give detail info as explained to me.
We should know that IOM Nigeria can not directly get your booking done for you.
Before you can contact them,you need to have gotten your stamped VISA.
After contacting them,a form will be sent to you as a principal applicant to fill in your details as the lead passenger.You will be expected to attache the biodata pages and stamped VISA pages of all intending passengers.You will also be asked to state your intending date of departure and final city of arrival in Canada.
Without the biodata pages and stamped passports,they WILL NOT attend to your application.
When all this is done (either physically or by email),they will correspond with IOM Ghanian office who is directly in charge of make such booking.The IOM Ghanian office advice the Nigerian office on the booking and the fares involved internally which is now passed to the Nigerian applicant.The IOM Nigerian office contact you back with the fare's information,estimated cost and account information for you to pay it in.
When payment has been made,the IOM office in Accra again issues tickets after payment confirmation and this is forwarded to the applicant via email.
No matter the urgency,we (applicants) all advised to give about TWO OR THREE WEEKS for the above process to be accomplished as the Nigerian IOM office to do not have full control over it.
If you are Ghanaian based,you can bypass all the procedures above and get your rates from them within 2 days.You can also fly to Ghana to correspond with the IOM office there.
Also,it is advisable that you don't contact them for a 5 month flight plan...try as much as possible to contact them when you are sure you want to move between 45 and 60 days....reason been that they want to be sure you want to use them.Giving you a discounted price 3 or 4 months ahead may make you change your mind and they would have worked for nothing so I will advice applicants to contact them between one and 2 months of your proposed plan.
The average amount depends on time peak in which you are travelling but they will generally get a somehow cheaper rate for you.
It also depends on the age of the children involved because children under two years pay lower(about 10 to 15% of adult fees),children between 2 to 12 years pay higher(about 75% of adult fee).
The waiting period is always to the advantage of the applicants with respect to the cost of flight so you should expect a fair bargain.
Cheers.