Both cases are good choices. Ventilation, airflow, and cooling capacity are excellent. I would recommend the Coolermaster CM 690 becuase it is a little larger than the Antec Three Hundred. There would be less of a problem installing the tall tower style cpu heatsinks and long video cards. Cable management is a little better too.
Lian Li which is well known for their aluminum cases has a subsidiary called Lancool that offers less expensive steel cases with plastic front bezels. The interior of the cases have some really great features found in the more expensive aluminum cases. They just came out with a new Dragon Lord series of cases suitable for gaming. The cases look like they have great potential. Some of the new cases are within your budget:
Also, there is an extra PCI slot cover, for adding USB, Firewire
and/or eSATA PCI brackets without obstructing the motherboard's
Cable management is a whole lot easier with the HAF-922 also,
because the holes in the motherboard tray are larger. We had
no trouble threading numerous cables from a Corsair 750W PSU
through similar holes in the HAF-932: