Re: Cost is the smaller concern
Citation needed as to your assumptions.
Personal expoerience with open- and closed-source code.
The difference is:
Open Source - developers look at it and say "fuck me, I'm not touching that crap"
Closed Source - developer looks at it and says "fuck me, I'm paid to maintain this crap?"
Have a look at the work being started by https://www.coreinfrastructure.org/, an advocacy group in the Linux Foundation, that is looking for sponsorship from big industry players to pay developers to work on essential FOSS code, because there aren't enough competent volunteers who want to do it.