HDP is hundred percent Open source Apache 2.0 licensed. When you download the product, you will be asked to fill a form. Please provide correct information and someone from Hortonworks sales team will reach out to you to discuss support options that you can get.
for personal use, you dont need to pay for anything unless you want paid support instead of relying on the community to help you.
for corporate uses, many organizations opt to use the HDP subscription to obtain paid support. There are varying levels of support & SLA's + varying levels of support based on the components (core vs. premium such as storm, ranger, knox, accumulo, atlas, etc)
Would require your answer here
After the merger of Horthonworks and Cloudera, I would like to know about the support subscription cost of HDP. Is it the same which Horthonworks used to display on website or is there any change. What are the various supports now are they offering.
Your best resource would be to contact sales for the most up to date information.