For a normal business hours support contract, you pay $349/year for RHEL or SLES, and $750/year for Ubuntu LTS for similar class of hardware.
For a 24/7 support contract, you pay $1500/year for SLES, $2500 for RHEL and $2750/year Ubuntu LTS.
Even though Ubuntu LTS is also available for free, and RHEL has a free CentOS spinoff, prices are not that much different and Ubuntu LTS is not cheaper than RHEL or SLES.