An hourly rate would be great, but if you do them daily, you will likely get a good system down and do it rather quick and might prefer a set price! If you don't have to worry about water, more is better. Heat will make your work area hard to see in, but once you know the motions, it's your best friend!
We never have had freezing problems here (not to brag), but I would think that can ruin your night!