I can only speak of my rehab, but it was a 6 week outpatient facility and the cost was about 7 grand. Best money I've ever spent. Inpatient rehabs are much more expensive, naturally.
Have you tried to taper yet? It can be very hard to do so but if you can, it can help so much. I have tapered in the past from a huge amount of norcos and I felt little to no withdrawals. There are also other things that can help such as clonodine. You do need a prescription for that though. Make sure you stick around this forum. You will get so much support and no one here will judge, just help.
How many are you taking a day and what mg?