There are two different types of operation for a cruciate. The cheaper option is usually around the $2500 mark and the better option is typically around $4000(TPLO or Tibial Plateau Leveling Osteotomy). The biggest problem with both types of surgery is there is a big chance that the dog will end up needing the other leg done too - off the top of my head the stats are around 60%, so you have to go through both the cost and the 6 - 8 weeks of crating for recovery twice a lot of times.
I opted to just manage the injury rather than operate but that isn't always an option, depends how badly damaged the leg is.
(now i just read you've already done the surgery. Good luck, I hope it works for your dog)
