Survey123 is included with an ArcGIS Online subscription; in particular the survey author must be a 'Contributor' (Level 2 user). If the survey is shared privately, the submitters must also be a Contributor as well.
Jackie, I have just gone thru that with 30+ users, there is a fee for each license, based upon a year's license fee.
Free for public, non commercial use, as in, you can create a survey and let the public submit public info for just transaction/storage fees.(usage credits)
Using it for an organization will cost you a license fee for each additional contributor (besides the 1 license included with desktop) in the $500 us dollar range, which includes a lot of usage credits. I don't know why ESRI doesn't make this public.