WWYD? re: CS (long)

CPA04

STBXH is disagreeing with the amount of CS he should pay.  When we submitted our financial records and the amounts were calculated, it came to $398 per month based on the income he submitted (LO's expenses do not go into the calculation at all unfortunately).  Now that he's unemployed (and choosing to stay unemployed so he can get the amount lowered in the decree) he says he can't pay that much, but would agree to pay $350 per month instead.

Other pertinent facts:

**I have offered to do half the transportation of B even though he chose to move away, which means an additional 420 miles per month. (you do the math on the cost of THAT gas and depreciation on my SUV)

**When he does get a job, it will most likely be cash under the table, so who knows if I'll ever be able to prove that the amount should go up or that he even has a job.

**He can somehow afford 30 packs of cigs a month plus the data plan on his iPhone among other things.

**If I don't agree to lower it, he threatens to take the whole thing to trial so he can get half my 401K (it would be about $15K before taxes/penalties) and I know he'd get it.

I should just suck it up and take the $350 right?  I know $48 a month isn't much, but it is almost $600 a year and over time, it would add up.  It's almost one more day of daycare per month (daycare is $54 a day...) or an entire tank of gas.  I'm sure I would feel differently if I was rolling in the dough on my own, but alas...I'm pinching pennies to the MAX and then some.

I would fight it but don't want to lose my 401K - that's really my only exposure and he knows it.

WWYD?  Take the $350 and shut up?  Work the wording so I do less transportation and in turn save the gas money?  Start playing the lottery so I don't have to worry about all this?