Not REALLY that expensive, if you plan ahead. I've been squirreling away spare cash for a PS5 off and on for a couple of years now, so even if it costs $100 more than expected it won't be all that painful.
I bought my PS4 in 2014, use it quite often so maybe averaged out it's about 2 hours a day, maybe a bit less, so let's go with 700 hours a year. That's 4200 hours over the past 6 years. $400 to buy, works out to $0.09 per hour of entertainment. Pretty cheap, IMO.
What gives me pause, this time, is that for the past year or so my PS4 is getting significantly more laggy in everything it does aside from running a game. The menu doesn't respond quickly anymore with a perceptible delay between a button press and the action happening, launching Youtube or Netflix seems to take longer and longer as well. The hardware itself is still solid, and so I suspect that the updates are the cause. That, and efforts to cram other services down my throat. Why do I have to be subjected to things like 'Playstation Now' or the Disney+ channel or 'Prime Video' if I'm never, ever, going to use them? From what I can tell, most of the delays I'm experiencing appear to be caused by thumbnails loading for the abovementioned services, and God-knows-what-else it's trying to do in the background. The recent Holiday sale installed a shortcut to the menu without asking, and while harmless, it seems a little intrusive for some reason. I guess this time will be based on how much I can control that kind of BS...
I'm not optimistic.