Normal captchas: from $0.5 to $1 per 1000
Normal captchas are captchas when you need to type the text shown on image. Rate is related to service load. If the load is low price is lower. If the load is high then rate increases. Statistics show average rate per hour during last days.
Big captcha, ReCaptcha v2 images: $1 per 1000
Big captcha is an image that has sum of height and width more than 400px. Rate is fixed to $1 and not related to service load. ReCaptcha v2 images - images from ReCaptcha where you need to select corresponding squares.
ReCaptcha v2 token: $2.99 per 1000