Intended use for the mtn bike? I ride mine in the dirt up mtn trails so I don't keep it nearly as clean as I do my roadies.
I wipe it down with a wet rag, then dry. I do clean off the drivetrain with WD-40 (pretty cheap stuff). I saturate a rag and run the train backwards through it to rempove excess gunk. I also floss the cogs witha WD-40'd strip of rag to keep clean. I let it dry over night then relube before hitting the dirt trail again.
I do have a chain cleaner from Performance, not very expensive at all. Not the $40 one!
, the cheap one works well!
Mtn bikes get dirty but the main thing is to keep the drivetrain clean and working crisp.