April 1, 2004, Google launched a free email service with 1GB storage. They released it to a few thousand users and the only way you can get an account is to get an invite from someone who already has an account.
There are two reasons why Google did this.
- This allowed them to scale predictably. They can release new invite codes at a controlled rate.
- They were able to grow exponentially. Because the invites were limited, everyone wanted one.
Many SaaS products began utilizing the same technique and you should also do the same. When you are an early-stage product, your users would be more forgiving to the bugs in the product.
You can give it away for free or if you want to charge, try to create a lifetime deal or a cheaper annual plan.