Plus that you are not making any third party aware of anything, as you don't need them. And might save you a lot of hassle in the middle of the night and you need vendor support, which generally at such hours could generate even more cost.

In my humble opinion, technical pov, the more you do in-house, and the less you rely on third parties, the more freedom the company has.

Also any in-house developed product, could be sold, generating income. Also, i believe, that developing your own, gives you a certain knowledge which you don't get if you are simply adopting third party software.

It's of course way easier/more clear to calculate ROI when you spending specific amounts instead of investing in knowledge, control and self power. The returns on that can very a lot.

But, generally speaking, things are only 'expensive' if you think they are not worth it.