Motel-One in Garching-Hochbrueck is just one Underground hop north of Allianz-Arena and directly at the station. That Underground (U6) goes to city centre aswell.
Problem is that it's a pain to go there/from the airport - a taxi is 50E each way, maybe a bit premium to get a taxi-van for 5 of you.
Next to it is also an Ibis and Ibis-Budget.