You should be able to create an additional PayAsYouGo subscription in the same Azure tenant parallel to the Azure student subscriptions.
This way you won't loose the benefits of the students subscription.
It's possible to copy the VM from one subscription to another. There are a few How-Tos around in the internet. One is this one:
If you create a new PayAsYouGo subscription it's an additional one. The existing subscription for students should be still available.
In a PayAyYouGo subscription you can work with a
Cost Alerts to control the costs.
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