There are 3 kinds of nodes (seed, witness, RPC). For executing API calls on my own server I would need a (full) RPC node. If I should become a top witness in future, I will start my own RPC node. The required hardware for running such a node is very expensive (would need at least 256 GB RAM (better more) ~ $240/month on privex.io + $200 setup fee).
One of the next steps for me is starting my witness node. Since we now/in near future need a 64GB RAM machine + 240GB SSD + extra server for the seed node, it's not super profitable currently, but maybe I will receive enough votes to reach the top 50 fast.
My costs are really at minimum and I don't think that I can really optimize them. The rent for my tiny apartment is ~ 240€/month (including warm water, heating etc.) I'm currently living a very minimalists life...