If you want to create HubSpot forms, yes, you need to buy the full marketing software.
If you are happy to use third party froms (for example Contact Form 7 or Gravity Forms on a WordPress website), HubSpot Free will collect the data from those.
So based on what you say, Collected Forms should be available for my account "Free plan"?
Because i followed the steps and went to:
click the Sales dropdown in the upper-left to switch to Marketing > then navigate to Collected Forms. If you do not have this option, you can enable Collected Forms by navigating to Account Menu > Settings. Select Products & Add-ons in the left sidebar, then activate Marketing Free.
If you want to create HubSpot forms, yes, you need to buy the full marketing software.
If you are happy to use third party froms (for example Contact Form 7 or Gravity Forms on a WordPress website), HubSpot Free will collect the data from those.