Why don't you use any other RPC node?
Also, carefull highload optimisation could make miracles. You could forward RPC requests to remote RPC node (zero costs for maintaining) and caching them on fast Redis DB. So you could lower you hardware costs dramatically without raising latency for 98% of users.
Why don't you use any other RPC node?
That is what I do. You can choose the node you want to use in settings on SteemWorld. But RPC nodes don't come with all features which I need in my tool. Mentions, follower history, incoming delegations, delegation history, transfer and content searching in posts, comment counts, witnesses produced block ratio, voting stats and many more things are only possible by parsing the chain by myself and storing the data in a fast db on my own servers.
Of course it is possible to develop own API calls, but that would require to run an own full node.