I actually don't see a way to delete a project once created either.
You can delete your project navigating to the billing page inside a project. To delete your account you can send a support request and we can process your request (described in the privacy policy). We'd like to automate it more, however we'd like a formal opt-in via email of the account/team owner when deleting backups and stateful workloads right now.
Addon disk pricing is the same as our volume pricing for services.
The disks are SSDs. We've added a margin on-top of GCP, EC2 and Azure SSD pricing so I wouldn't say they are expensive in comparison to other providers.
It's possible to configure HDD storage which is much cheaper, would be happy to enable that feature flag for you. SSD $0.30 per GB, HDD $0.15 per GB. We'll add HDD pricing to the site and start to enable it by default for everyone.
I was looking for somewhere I could run web services and cron jobs both in the same place.
They have a Heroku importer, however I think you need to ask to have it turned on. I found that it was easier for me to build docker images for my apps and use a 'build service' instead however. YMMV
I found their support to be very responsive and enjoy using their UI. The UI, builds and so on all feel very fast.
Northflank can run databases, however for my databases I've been running them on ElephantSQL for some time (https://www.elephantsql.com) - even when I was on Heroku.
Free for Dev's PaaS list is worth a review: https://free-for.dev/#/?id=paas