You can use Testable to create an unlimited number of experiments and surveys, but you can record only 20 results for free.
For more, you need to purchase credits for $0.50 each.
With a subscription, you get unlimited credits for free (Premium) or 500 credits for free and additional ones for a reduced fee of $0.30 per credit (Plus).
With a departmental license, you get unlimited credits for free.
There is also a limit for 100MB that applies for your stimuli. With a subscription, this limit goes up to 1GB (Plus) or is removed (Premium). There is no limit with a departmental account.
Additionally, with any subscription or departmental license you get premium support, with a guaranteed first response within 24h.

Payments, Credits and Minds Budget