If they ramped that $5/month to $20/month after X months, I would keep paying it. Digital Ocean is a fantastic deal, everything I've tried straightforwardly works, and the fact that I can't accidentally spend money as I experiment is a real boon.
I would definitely have signed up for a competitor if DO droplets cost 400% what they do now. As other commenters have said, this space is a brutal race to the bottom in pricing. DO is great, I might pay 50% more for their current services, but not 300% more.
As someone doing proofs-of-concept and experimental work, the resource I'm trying to conserve is my own time, and Digital Ocean's value proposition on that is great. Everything works really straightforwardly and I can concentrate on my own code.
I wouldn't suggest Digital Ocean change their high-volume pricing, but the experience they provide to the small-scale user is worth a premium.