Can’t speak for southern border CBP, but DFW airport guys are “well paid,” according to a classmate from the area. Might be able to get more from other fields, but he felt he got into a good place with this.
We have a few going to Laredo, San Ysidro, and some other well known spots. Never asked them about specifics with pay, but you should be able to find pay scales online.
One thing, most southern border positions offer decent pay incentives. Unsure if they are still doing it, but a 33% incentive paid upon hiring, and same payment for the following two anniversaries of hiring (doesn’t increase over time, same 33% of first year salary is paid for the other two). Have to stay at the port for 3 years... or pay it all back. Some unpopular northern ports had 25%... which is what I signed up for.
If you get sent down south for TDY... it is a decent pay. One of our instructors was breaking it down for us, and was actually a decent chunk of change. If I had the option... I wouldn’t want to go. But if my number is drawn, I’ll make the best of it.