For a new F30 you'd be looking at maybe 10k per month financing it. So the OP has to spend 10-20k on shocks now and then he's good (shocks wise) for the next 100,000km...
There is no need to maintain a car with OEM components. I would definitely consider the Koni option from Axis. I did many years ago and have never looked back.
shock degrade more over KM than time my guess is the OP does alot of KM that is also why his car is off MP in general shocks should last 100 000km
Errol I can also supply Sachs they make shocks for BMW OEM lead time is a bit longer on the F30 because they only do sea shipping but price will be less than Koni