The MLX90614 contactless thermal detector has a 90 degree field of view (although variants with narrower FOVs are available) and is now down to about $15 on ebay, or $20 from U.S. distributors: Pololu - MLX90614ESF-AAA Infrared Temperature Sensor 90° FOV
They give you the average temperature of the entire field of view but can easily detect lightly clothed humans a meter or two away. As the distance increases they work less well at detecting humans, but that seems appropriate for your project. The response time is a few tenths of a second.