It's going to cost you more than that...
$2500 application fee + $4000 yearly fee just to be an ICANN registrar. Then they charge you $0.20 per domain. And here's the real cost... you have to still pay a per domain fee to each gTLD registry... for instance currently .com domains will cost you $6.42 each, .net will cost you $4.60 each, .org costs you $6.15 each. That means @ $10/each you'll only be making $4 or $5 per domain before you even factor in the ICANN fees.
In addition to this... you have to setup whois servers or purchase this service from someone. For instance OpenSRS.com offers what they call OpenHRS.. note the "H", not to be confused "S" which is their OpenSRS program. To become an OpenHRS partner with them, I think they require you to first have been an OpenSRS reseller and have 30,000+ domains before they even talk software pricing with you.