Budget:20$,please do not bid more than 20$.
You should have experience with Digital ocean,UBUNTU.
1)Server becomes slow at peak times ,need to configure nginx, hhvm,redis,load balancer.
2)Already site is running with nginx,hhvm,redis but slow.
This is 1 hr job for expertise.
3)Server is having 8GB RAM
4)you can find out logs and make it faster so that server responds quickly.