As Pablo said, I would recommend having a horizontally-scalable cluster. Start off with 1 nginx load balancer, 2 nginx webservers, and 1 database server (2GB would be fine, but it mostly depends on your application).
The total monthly cost would be about $35 if you go with 512MB droplets for the load balancer and the webservers. Nginx should handle a lot of load on 512MB so I'd say you start off with a 512MB load balancer and two 512MB web servers, and scale up as needed by adding more webservers to the cluster. You can either create a new database server with master-master replication or scale your database server to the next plan.
Once you reach the point where one load balancer is not enough, add another load balancer with its own set of webservers and have it on a round-robin DNS setup.
Even if you do that, it would still cost you less than 1/3 of what you're currently paying.
Let me know how it goes :]