Instead of paying for monthly or yearly upload quotas, you can simply pay for upload quota one project at a time.
When creating a new deliverable in a project, you can choose the amount of quota you need from the available options. You can start with a free 1GB upload quota option and purchase more upload quota later. Or you can purchase a paid higher upload quota option (for example, 10GB for $9 USD). You can then upload up to 10GB of media in that deliverable.
You can add additional upload quota to any deliverable for $5 per 5GB of additional quota.
Note: Deleting and re-uploading media (i.e. replacing media) also counts against your quota.