JERRY: Well, that's... that's... I'm not go inta, inta... see, I just need money. Now, her dad's real well off.
We never learn the nature of the original debt Jerry needs to pay off: the Coens kept it intentionally obscure. But obviously he's willing to hatch some dangerous, crazy plan to get money.
JERRY: Well, it's all just part of this - they don't know I need it, see. Okay, so there's that. And even if they did, I wouldn't get it. So there's that on top, then. See, these're personal matters.
CARL: Personal matters.
JERRY: Yah. Personal matters that needn't, uh –
CARL: Okay, Jerry. You're tasking us to perform this mission, but you, you won't, uh, you won't—aw, f*** it, let's take a look at that Ciera.
Carl's greed makes him overlook Jerry's secrecy about his motivations for the kidnapping. If he would've pushed, he might have seen that Jerry was a pretty desperate and pathetic guy who hasn't thought this through at all; he could have backed out of the scheme. But he wants the car.
JERRY: No, see, I don't need a finder's fee, I need a... finder's fee's, what, ten percent? Heck, that's not gonna do it for me. I need the principal!
STAN: Jerry, we're not just going to give you seven hundred and fifty thousand dollars!
Jerry's hoping he can pay off his debt through this deal, instead of going through with the kidnapping scheme. Jerry's not satisfied with Wade's offer; he wants the whole enchilada. We don't know how generous Wade's offer would be, but given his business savvy, not to mention his feelings about Jerry, maybe Jerry knows it wouldn't as much as he needs.
WADE: Well, look, I don't want to cut you out of the loop, but this here's a good deal. I assume, if you're not interested, you won't mind if we move on it. Independently.
It's hard to say what Wade should've done in this case. Technically, he's offering to give Jerry a certain amount of money, but it's not enough and it might not be in proportion to what Jerry actually did by bringing the investment to his attention. Wade doesn't realize that he's effectively dooming himself and his family, causing Jerry to move forward with the kidnapping plan.
CARL: Jesus. Well, it doesn't matter. I got the money. All of it. All eighty grand.
Carl's lying to Gaear. In reality, he found a million dollars in Wade's suitcase and hid it in the snow. "Well, it doesn't matter," is Carl's comment about Jean's murder. It doesn't matter because they don't need a live Jean to collect the ransom anymore. She's no longer necessary.
CARL: How the f*** do you split a car, ya dummy? With a f***in' chainsaw?
GAEAR: One of us pays the other for half.
Gaear kills Carl after this argument over a car because Carl flips out and escalates the argument. But Carl just stolea million dollars. The car should've been a non-issue at that point, ya' think? Greed has totally taken over.
MARGE: So that was Mrs. Lundegaard on the floor in there. And I guess that was your accomplice in the wood chipper. And those three people in Brainerd. And for what? For a little bit of money. There's more to life than a little money, you know. Don't you know that? And here ya are, and it's a beautiful day. Well, I just don't understand it.
Marge probably does understand it. She's a savvy cop who's probably seen plenty of "malfeasance" over money in her day. But it's so far out of her own value system that she's still amazed when it happens.