Very cheap means that I pay 300 euros annual fee and get paid over 3000 euros per quarter if something happens, which I hope won't. And I can keep it if I change employers.
That's not exactly "cheap"...
So you pay 25€ for 1,000€ disability insurance/month - sounds normal to me.
For example, I pay 54€ for 1600€ disability insurance, but now increase it to 75€ for 2100€ disability insurance because of house construction.
When applying the rule of three, you would find that with more than double the contribution, you only get 60% more performance. Apparently still cheaper than your insurance?
The contribution of course also always depends on which profession ([Gefahrenklasse]), at what age you start, which additional benefits exist (e.g. [Todesfall]) and so on. The pure comparison of contribution - BU pension is therefore, in my opinion, not very meaningful.
applying a rule of three in comparison makes quite little sense for the reasons you already mentioned. Other factors like profession/age or pre-existing conditions also play a role.
What, in my opinion, should also be said is that €1,000/month may be cheap, but certainly not sensible. I think hardly anyone as the main earner & builder can manage with €1,000 occupational disability pension.
What I would be interested in is up to which age you are insured?
I currently have an old disability insurance with a contribution of 48 € / month, 1250 € until 65 years old. At 50, the payments with a burden of 1,300 will expire, I am considering giving this up and taking out a new one with 1850 €, but until 60 years.