Hi,
All ArcGIS Developer Subscription plans from Lite upwards include access to the ArcGIS Runtime SDKs for development purposes. For more information see:
Compare Plans | ArcGIS for Developers (Building Apps)
Compare Plans | ArcGIS for Developers (Extending the Platform)
To license ArcGIS Runtime for deployment your customer can either use the free license key (Lite only, non-revenue generating apps), purchase deployment packs (Basic, Standard, Advanced, and Extensions), or license the app at runtime by signing in as an ArcGIS User. For more information see:
Licensing your ArcGIS Runtime App | ArcGIS for Developers
To purchase Basic, Standard, Advanced, and Extension licenses, if you are a US customer please contact Esri Customer Service or call 888-377-4575. If you are outside the US, please contact your local Esri distributor.
Regards
Mike