"Call me if you ever wanna do a bounty... it's a good way to make some money... (nervous/awkward laugh here)"
Lester is saying you can ask him to set a bounty for you, and since it costs $1,000 extra to place a bounty, and he's the one placing it, he makes a grand. It's like this:
"Call me if you ever want to [set] a bounty... it's a good way [for me] to make [$1,000]. (laugh to fill the silence/he doesn't know what to say, a 'Yeeeaaahhh... laugh')"
Good theory, and would be apt excuse if you worked for R*
Fact of the matter is, it was probably just a dialogue error. Bounties didn't always cost an additional thousand if I'm not mistaken.
It may of been an error..
OR (bare with me)
I'm pretty sure its implied like this..
"Call me if you ever want to set a bounty on someone... [pause] it's a good way to make some money (claiming a bounty that is)."
Why this had to span 3 pages for an answer, I don't know.