What is the difference between Splunk and elk stack?

Can you please clarify the key distinctions between Splunk and the ELK Stack for me? I'm trying to understand how they differ in their functionality, ease of use, scalability, and perhaps even their pricing models. Is one more suitable for real-time analytics compared to the other? Also, how do their integration capabilities with other systems and tools compare? I'm looking for a comprehensive overview that can help me make an informed decision on which platform to adopt for my organization's log management and analysis needs.