If I develop an app/add-on that allows my application to interact with Splunk, is there a cost for me to have it available on Splunkbase? Does Splunk charge users or developers for the use of apps/add-ons?
Yes, it's free. You can host your app on Splunkbase or externally. See Options for submitting content in the Working with Splunkbase manual for details as well as links to developer documentation and information about certification.