I posted this as a comment in response to a couple of other comments (thank you, Kalleigh and Meno!), but since I'm not clever enough to figure out how to save my comments in PDF when I save my blog, I wanted to post this here (with a couple of small additions) for future reference.
(In reference to the thought of giving K full custody of J and me getting a second job) I'm not sure how that would work, given the current logistics - this is why K doesn't keep J during the week as is, as it would be very difficult for him to get J to school each day given where he lives and where he works. I could ask him to keep J some nights so I could get a second job, and we have discussed that (he and I have - not sure if I've posted about it or not). But I think the switch from all the time with mama to all the time with daddy would be too abrupt for J - he's a creature of routine, and it would disrupt him mightily to suddenly be at daddy's house all the time (even if the logistics worked out OK). Something to think about, but I'm not sure it would work out in practice. Thank you for the thought, though, and if you've got any more, feel free to share 'em.
The challenge would also be, with a second job, finding one that paid enough to do any good. If I get a retail job for 10, 15, 20 hours a week paying $7 or $8 an hour, by the time taxes come out of it, I'm not sure it accomplishes anything other than leaving me slightly less in the hole and having almost zero time to spend with my son. So unless I could find something part-time that paid enough to make a real positive impact, it's not worth the disruption of having K keep J all the time.
I sell Pampered Chef - if I could just find the time to put some effort into promoting that, could I make it work? People do, but do those people also work full-time? I don't know. I do calligraphy. I make candles. I do all sorts of little crafty, gifty things that could be potential money-makers. The trick is, finding time to do them and promoting them so that I'll actually make money.
(In response to Meno's comment) Right now, it does feel fairly overwhelming. And what really makes me kind of sad is that K and I suffered and limped along financially while he had a crappy job that was basically temp work (the job itself was decent, low-stress, not fabulous pay but not horrible, he could work there as long as he wanted, and it was 40 hours a week when there was work to do, but they might run out of work for days, weeks, months, and that can pretty well destroy any semblance of a budget) while we were married. If we were still together right now, given that he's now got a good job that pays decently, we'd be doing all right, maybe even kind of sort of well. And that sucks the worst. Things were hard when I was married. Things are hard (hell, harder) now that I'm not married. When do I quit feeling like the butt of a giant cosmic joke?
Yeah, I'm in full-out whine mode right now. I freely admit to wallowing in the pity pit.