well you have 2 options:
Tokina 10-17: Fisheye ~$400?
I dont know too much about this lens, but my body has it and he likes it a lot. I'm not big on fisheye
Tokina 11-16: Ultra Wide Angle (no distortion, just wide as fuck) ~$550-600
Beautiful lens, had this on my T2i before i went fullframe. Built with cinema specs or something fancy like that, amazing IQ quality. The best UWA sub-$1000 i believe
feel free to correct me if im wrong