It might be challenging to get a sensible priced one for what you are describing. It would probably need an autel or something.
You can perhaps get a windows laptop and some bmw software and an obd2 cable.
By the time you have purchased all the diagnostic equipment, what is the cost delta of diagnostic equipment, the parts and your time vs a repair cost from BMW or the garage.
It’s worth getting some quotes.
If you already have a windows laptop, then might be better. No idea what software is needed or where to get it. Thats where the power of the forum comes in!