You get the same shocks with internal teams, just from other causes. And you have to manage them.
I'm sure you've only ever seen brilliant software created by internal software teams?
I have no idea how you are spending "large amounts" of unplanned spend on Saas products. Every company I worked for had Saas subscription costs being under 1% of capex. Unless you add AWS, which is actually "large amounts" but good luck vibe coding that.
We had an in-house system that worked, but it was a two pizza team split between time series and logging. "Internal weirdware" got thrown around a lot, so we outsourced to SignalFx for a few years. It was bumpy. I liked our in-house system better, and I didn't build it.
Splunk then buys SignalFx and immediately multiplies the pricing at a conveniently timed contract renewal. Suddenly every team in the company has to plan an emergency migration.
Your supply chain is messed up. You need sign longer contracts with price guarantees.