$ host cheapoair.com
cheapoair.com has address 70.42.217.150
cheapoair.com mail is handled by 0 fareportal.com.s9a1.psmtp.com.
cheapoair.com mail is handled by 20 fareportal.com.s9b1.psmtp.com.
cheapoair.com mail is handled by 10 fareportal.com.s9a2.psmtp.com.
cheapoair.com mail is handled by 30 fareportal.com.s9b2.psmtp.com.

$ host insanelycheapflights.com
insanelycheapflights.com has address 54.243.140.73
insanelycheapflights.com mail is handled by 0 smtp.secureserver.net.
insanelycheapflights.com mail is handled by 10 mailstore1.secureserver.net.

$ host onetravel.com
onetravel.com has address 70.42.217.118
onetravel.com mail is handled by 30 fareportal.com.s9b2.psmtp.com.
onetravel.com mail is handled by 10 fareportal.com.s9a2.psmtp.com.
onetravel.com mail is handled by 20 fareportal.com.s9b1.psmtp.com.
onetravel.com mail is handled by 0 fareportal.com.s9a1.psmtp.com.

Looks like onetravel.com and cheapoair.com is owned by fareportal out of NYC. Onetravel.com hides their domain registrar though but their email servers line up with cheapoair.com.

Insanelycheapflights.com is registered in Ashburn, VA to Esteban Oliverez. So might be different company.