In my experience, you can grab a lot of guys away from a SIM of equal or lower prestige for about 12-14K.
However, if the guy you are pursuing is the SIM's primary target, it can cost a lot more. I once spent about 40K to win a battle against a SIM. The guy was about 200 miles from me and the SIM had B prestige while I had B-. He was considering me at about 20K, but I didn't take the lead until 38-39K.