Actual Cost to Domain Registrar?

Hello everyone. I just reached here today. I was wondering that with all those great deal offer by the domain registrars like 1and1, registerfly...etc, with their promotion price of cheap domain regostration eg $2.99 for .info has been going like hotcake! How could they still make money and earn profit?

So, what the actual cost to these domain registrars that they could still afford such low price? eg :-
1. Actual cost for .com?
2. Actual cost for .net?
3. Actual cost for .info?
4. Actual cost for .biz?
5. and so on?

or is it possible that these registrar are still under cost? Anyone has a good idea?

Thats a good quesiton, one that I really don't know the answer to, but I would be interested to here about it if anyone else does.