'Tec 837, as mentioned. Also, probably not coincidentally, the last time Eddie wasn't a complete chump. The actual amount paid is never mentioned, but Bruce hired him, and there were several points that made it clear he was paying a huge amount.
First, Bruce, when hiring Eddie, says 'I'm in need of your service, and your silence. I'll pay well for both.' As Eddie charges 25 grand for a routine following of a spouse (as mentioned a couple panels prior), clearly this would lead to his negotiating for something closer to 6 figures.
Second, he was able to buy the house that Boneblaster just wrecked up on him. Which could have left him down to just the (still pretty good) cash from his regular detective work, except for...
The third point: When Bruce and Tim are discussing the case afterward, Bruce says that, on top of testing Eddie's skills as a detective (passed the test, contrary to what later issues would suggest), he was making sure Eddie was living comfortably enough to reduce the chances of his going back to crime. Also...
Fourth, Bruce believed that the fee he was paying him was enough that it took away the temptation of absconding with and selling the rather potent super-steroid he was hiring him to retrieve. Which would have to be pretty big bucks.