A detailed pricing breakdown of Zapier is available here. Zapier starts for free and the pricing goes up to $5000 USD per month for the highest plan. Please contact Zapier for more information.
To give a rough idea, if you trigger contact creation for 500 leads a month, it would cost $19.99/month (billed annually). If you use a workflow that triggers contact creation for less than 100 leads a month, it would be free.