Wa `alaykum As-Salamu wa Rahmatullahi wa Barakatuh

 

If one made an agreement of sale between him and others even friends of a certain amount and they agreed to it and then he was able to bring it cheaper, he can keep the extra 2 as a profit.

 

Now, this is what merchants do, they sell goods and make profit out of it.

 

If your intention in the beginning was more of a service with no plan to make money off your friends, it will be a good ethical practice to tell them the real cost and let them decide if you are to keep the extra 2 or return it back to them.

 

Almighty Allah knows best.