It’s really hard to pinpoint how exactly it’s going to cost. There are a few factors that you need to take into consideration. First one is the required specs :
OS: Windows 7+, OSX 10.6.6+, or Ubuntu 18.04.
CPU: Intel Core Duo E6600 (2-2.8GHz+) or AMD Phenom X3 8750+
You’ll need to find the same server in DigitalOcean for that. Looking at the droplets, it seems like you should be able to host the Counter Strike server with the 20 or 40 dollars per month plan.
Having said that, please note that additional bandwidth is actually paid so you won’t necessarily pay 40 dollars per month but more. To get a better perspective on this, I’ll recommend giving the following documentation a read: