I think DigitalOcean probably bills Dply for one hour minimum so if you could immediately destroy and recreate then you'd quickly add up to a lot more OpEx.
How am I billed?
Each Droplet is billed per hour up to its monthly cap.
Do I have to pay the cost of the server every time I create a new one?
No—you only need to pay for 1 hour of usage. For example, spinning up a new 512MB server just to test something for a couple of minutes will only cost you $0.0074