You sound like you have perinatal anxiety. I'd speak to a doctor or midwife to see if you can get some counselling.
All these worries u have I had the same. In fact I took on other peoples worries etc like omg how will we fit in the car, how will we go on holiday. I only realised after the termination they were all foolish. I got pregnant again 3 months later out of guilt and now that baby is here and 7 months we just cope. You will too. You just adjust here and there to save money. Batch cooking, wear your clothes a bit more, buy less clothes, eat out less, walk more, use what you have etc etc
Your fear of having another difficult pregnancy and traumatic birth I had the same. My second pregnant was very tough with sickness and last minute breech. My next pregnancy I aborted because of those fear again but the pregnancy after that everything was fine.
I had a lot of guilt when I got pregnant with 2nd fearing that the joy of being 3 would be taken away but it was even more fun with us being 4...you just adapt and cope...it's human nature..
Fun money will be there maybe not so often but you will find pride and joy in other things. We discovered our library and museum which are free when our child was 6. Before we paid to go everywhere. The national trust stuff is there. We go on group on for soft play etc.
Would your son be sad he missed out on all those things (slight exaggeration I'm sure he could do those things but less often)or would he want a sibling?
I had pnd with first and it wasn't there with second but here with 3rd with a little bit of post natal anxeity...because you've had it before you know what to do and go to the doctors etc...you'll handle it better. I understand your fear...I really do...but remember it's the pregnancy hormones making u more anxious that you are...
The baby stage seems so long with your first... I can't remember it with my 2nd and third it went so fast because your first also had your attention and keeps u busy...if u think about it it's such a short stage. The first 6 weeks are hard but you get past them. You've done it before it will be easier.
I'd sit down and list all the pros and cons. I'd think about how you'd feel if baby wasn't there anymore and what if u couldn't get pregnant again. I'd also talk to a councillor. I'd also ask your son how he would feel if he had a new sibling. Don't ever base your decision on money. You could be a millionaire and plan 7 kids and have them then be homeless tomorrow. That's life. You don't know what's going to happen but you can take a risk for joy.