For hosting just general websites, on an unmanaged server, $1k / mo is overkill, even for two high spec servers. I would say $200 - $250 / mo should give you a reasonably powerful unmanaged server with cpanel from most reputable hosts, so $400 - $500 for the pair is a more realistic budget, especially for just starting out.
Now, on the other hand, if you're already hosting these sites, and you happen to know the specs of what they're being hosted on, then we could give you more specific advice here, as the actual specs needed for two different people, whose only specification is "500 websites" can be vastly different.