Compare two different costs
Cash has an obvious price: the money leaves today. Finance has a visible monthly payment and usually a higher total cost. The missing question is what the cash purchase would do to the business's resilience.
When finance can be rational even if it costs more
If paying cash would destroy the business's operating cushion, keeping some cash and accepting a manageable monthly payment may be worth the extra finance cost. But a repayment that consumes nearly all monthly breathing room creates a different kind of fragility.