To publish one app, you need the builder plan.
Also, to publish an app to the App Store, you will need to have an Apple Developer Program membership, which costs $99 a year.
You can read more about publishing your Thunkable app here.
To publish an app on Google Play Store, which costs $25, you need to download an AAB file and upload it to the Google Play Store. Please follow the steps here:
You can publish your app as a Web app without extra cost: