What kind of Control Panel are you using? If using Cpanel I would use CSF for Firewall... if you budget is low.. Preventing attacks is more hardware than it is Software. But software does help aswell.. I'd look into some kind of DDos Deflate or alike.
CSF is definitely a one shot answer in case of Cpanel servers, you can configure CSF with LFD ( login failure daemon)
Login Failure Daemon (lfd) process that runs all the time and periodically (every X seconds) scans the latest log file entries for login attempts against your server that continually fail within a short period of time. Such attempts are often called "Brute-force attacks" and the daemon process responds very quickly to such patterns and blocks offending IP's quickly.
Login tracking is an extension of lfd, it keeps track of POP3 and IMAP logins and limits them to X connections per hour per account per IP address.