There is a thread over on Eno's about the cost difference between 9Major and 38 super.
It can really be a push from a cost stand point as the super brass will last MUCH longer than 9mm loaded to major (you will need some sort of roll sizing set up and/or some special dies to process the case bulges out of 9Major brass).
If you want to get started in Open you shoot look at RO'ing or staffing a few major or regional level matches. You will have lots of opportunity to pick up 38 super brass at those matches and to see what the top shooters are using for equipment.