We are asked this constantly, and we do not have a rule that fits every business, but we do have a question that usually settles it: is your business run like most others in your category, or does it have a way of working that is genuinely its own?
If the exceptions in your process are rare and minor, ready-made software will almost always be cheaper and faster to get running, and we will tell you so even though we build custom software. If your exceptions are frequent and central to how you actually make money, forcing them into somebody else's software usually costs more in workarounds over two years than a custom build would have cost up front.
The quiet cost
The expensive version of off-the-shelf is rarely the licence fee. It is the parallel spreadsheet that appears six months in, because the software could not do the one thing that made your business different.