Several times I put $39 in the Mega Cash machine or the Wheel of Fortune and walked away with $150+ in my players bank. 25 machines and once I get $39 in credits I go play those credits on a $1 machine. I accumulate the credits that I've 'won' when playing.
The machines this past week I thought paid pretty good in that I would 'win' back about 90% of what I put in. I always go to the casino before it opens and set up my players bank so I'll be ready to go when it's time. I was on the Glory last week and as others have said you can put cash in the machine but can't get it out.