SageMaker Model Registry, Model Monitor and Hyperparameter Tuning jobs - Pricing?

There's no price for using SageMaker Model Registry - you only pay once you start hosting the models. For hyperparameter tuning jobs, you pay for the number of training jobs that the tuning job spins up, so you can plan accordingly in your pricing calculator (for example if you have 12 combinations of hyperparameters, then plan for 12 training jobs in the estimator). Similarly, model monitoring runs processing jobs on schedules (see docs).