Well there's a few different pieces here. This post is talking about the SCOTbot server specifically which is currently a centralized and proprietary software that uses the Steem Engine platform.
The Steem Engine platform is technically as decentralized as anything else - the code is open source and available for anyone to run and independently verify the state of the system. That can also be run on similarly priced servers. I should also note that a Steem consensus node also only requires about a $50 - $100 / month server so Steem Engine is pretty much in line with that.
Centralization vs decentralization doesn't typically affect server costs...an abnormally high server cost most often just means that the software was not designed to scale. Now that the MIRA project has been finished, among other things, the costs of running a Steem full node have also dropped to much more reasonable levels.