Seriously, building a AWS clone on DO infrastructure is just not possible. Even if it would be it would actually be more expensive in the end as AWS for small to medium projects. If you using AWS you do not only pay for one virtual server, you are paying for a infrastructure. You would have to replicate parts of this infrastructure, which would require a few separate servers and you couldn't share those costs with other users.
Using DO instead of dedicated servers for this would be like building a Uber competitor using the Uber API.
Edited: I overlooked the fact that at least neither Hetzner nor OVH do provide a useful (for this project) way to order a dedicated server via the API. They do offer an Order API, but the spin up time is too long.
That said, one of the reasons to use providers like Hetzner and OVH is that as I've pointed out elsewhere, the price difference is so large that most people who "need" auto-scaling at places like AWS would pay less if they just ordered 2x to 3x as much capacity at a place like Hetzner and left it on 24/7.
Very few people have loads that are genuinely spiky enough to save enough from auto-scaling to make up for the massive cost difference.
I don't have a clue how much harder this would be, but a price difference of about 300% looks much more interesting.