Is there a free tier or free usage allowance in Catalyst?

Yes. Catalyst enables you to select between two different pricing models: Pay-as-you-go or Subscription. You can avail a free tier allowance in the pay-as-you-go model, or a plan benefit in the subscription pricing model. Both these benefits provide you with resources for free of cost until you exceed the hard limits imposed for the specific resources, or for the overall amount consumption, depending on the model. Refer to the Billing help documentation for details.