Hobart-Era KitchenAids on ebay
I'm not looking to buy another mixer, but just for fun I looked at some listings on ebay for the KitchenAid K5A and K5SS. Both are 5-quart bowl-lift mixers.
There are some pretty good-looking deals on the K5A, a model made during the Hobart era and discontinued in 1978. Some are buy-it-now listings and some are auctions. Many are in the $100 to $200 range, including one that is ugly canary yellow.
Not all parts for the K5A are still available. Motor brushes and accessories such as dough hooks, beaters and whisks are still available. If the motor were to suffer a catastrophic failure you might be out of luck. I got a used K5A last year (a proper white one). I got lucky and it seems to have been a low-mileage unit and well cared for. I took it apart and gave it some new food-grade Teflon grease. It runs very smoothly now. If my K5A were to fail catastrophically, I would be out a little over $100, rather than much more for a more expensive mixer. It would still be sad to see it go, though.
The K5 mixers underwent a major design change in 1978.The motor controller was completely redesigned for the K5SS, the successor to the K5A ("SS" stands for "solid state"). The K5SS was discontinued just a few years ago, so it was kind of an overlap model between the Hobart and Whirlpool eras. It appears you can still get parts for the K5SS such as motor components and electronic parts.
There is no way I would buy a new Whirlpool-era KitchenAid mixer. I have read that the Whirlpool mixers use cast gears rather than the machined gears used by Hobart. Keep this in mind if you read a review complaining that the gears on a modern-day KitchenAid stripped.
It is my understanding that KitchenAids have always had a nylon failsafe gear going back to the Hobart era. It is intended to fail if the load on the mixer is too great. The idea is that this gear is easier to replace than the motor which could burn out if it could no longer turn due to a heavy load or an obstruction. Whirlpool used plastic gear housings (not plastic gears) for a time in KitchenAid mixers. This turned into a debacle with many failures. They now use metal gear housings.
I use a spiral dough hook (K5ADH). Officially it's not supposed to be used on a K5A or K5SS but I use it anyway. When kneading bread dough, a lot depends on dough hydration.
Here is an excellent video on changing the grease on a KitchenAid mixer.