If you're considering whether you can afford running more than one server for your business, you're likely to discover that you can't afford not to. Even with the additional operational expenses, you’ll be better off having redundant servers because redundancy minimizes downtime for your critical applications and reduces the costs incurred by outages, which can be huge. The price of downtime is always too high for any business.
Like it or not, IT downtime is a fact of life. Systems fail. Outages happen. The failure rate of cloud servers is roughly 2% annually, for example. The larger the installation, the more frequently outages will occur. The best way to deal with these inevitable worst-case scenarios is to be prepared and minimize the downtime as much as possible.