Kids do seem to go through a bit of an obnoxious phase at this age. I have a friend with a daughter of the same age who could have written your post herself. I sympathise.
Has anything happened to your DS lately? Might not be anything big, but sometimes even something fairly small and trivial can cause a child to behave differently. If not, it may be that he's just taken a step further towards developing his independence and unfortunately it's coming out as challenging behaviour. I'm sure you're doing a great job and this behaviour will pass eventually.
Don't want to sound completely patronising here but have you tried a reward chart? He gets a sticker every time he goes to bed without a fuss and when he gets four stickers in a row he gets a treat? I know money is a problem but the treat needn't be expensive. Or you could use treats such as promising to sit down and spend an hour making something together, or baking in the kitchen, etc. You can back this up by having a three strikes and you lose a privilege stick as well as the reward carrot. Does he have a games console you can confiscate or a favourite TV programme you can stop him from watching? Ideally though, it's best to concentrate on being positive.
About money, it's worth contacting your school. Some schools have a bit of a support fund that they can use to help lone parents.
Is there a lone parents group in your area? It's a great way to make new friends. The beauty of having other lone parents as friends is that not only do they understand the difficulties you face, but because there is only one other adult rather than a pair, you can stay over each others houses as you can be somewhat flexible and creative with sleeping arrangements.
Last but not least, don't beat yourself up about this. I don't believe there is a parent alive (whether single or paired up) who hasn't lost their temper with their children at some point. It's called being human. You're having a rough time and are entitled to feel crappy about it. It's so much easier if you can offload on to someone, even if it's over a forum or on the telephone, so keep posting when it all gets too much. In the meantime, think of your current problems a bit like labour: hurts like hell but it will come to an end.