It depends on what you’re comparing it to. On-premise systems avoid a recurring software fee, but shift the cost into IT staff time, server maintenance, security patching, and backup management, all of which have real costs even if they don’t show up as a line-item subscription.
Many on-premise vendors also require an annual support or maintenance agreement on top of the original purchase price just to keep receiving updates and technical support, so the “one-time cost” often isn’t as one-time as it first appears.
