Bayern can spend A LOT on a single player (e.g. Gomez, Martinez, Robben, Ribery) thru the years but they have also made some low cost transfers for key players like Dante, Alaba, Gustavo and even Mandzukic could possibly be put in that category.
Overall, iirc thru the past 3-4-5 years they have spent less on transfers than Juve, Inter and possibly even Milan ... forget about City, Real, PSG, Barca.