As far as the costs are concerned, that's true. But you're doing it at the expense of stability. Instability can break the bank even more. Think of not inaccessible site, updates issues, blown error logs, performance or SEO issues like de-indexing from the Google and so on.
I use and write plugins myself. But I check twice and triple if a "useful" functionality is indeed required. Or is it just a nice gimmick I can live without. This approach saves me a lot of time, that I can spend on community building instead of solving technical difficulties and playing ping-pong with IPS, hosting, and plugin developers. 😉