REW (free, but not FOSS): https://www.roomeqwizard.com/
A calibrated measurement microphone can be bought for 79$: https://www.minidsp.com/products/acoustic-measurement/umik-1 or https://cross-spectrum.com/measurement/calibrated_umik.html
A calibrated measurement microphone can be bought for 79$: https://www.minidsp.com/products/acoustic-measurement/umik-1 or https://cross-spectrum.com/measurement/calibrated_umik.html