i have been in this situation, although finance was not his reason, just feeling complete was.
My ds1 is 5.7, ds2 is 3.1 and dss is 6.1.
I wanted another baby when ds2 was 6 months, and argued and fought with dp for 18 months, until one day he said this has to stop. he said i love you but i just ant do this right now, i feel i have enough, etc etc. I explained how i was missing a pair of shoes, a plate, a coat everytime i looked there was 1 less than there should be. He said we could talk in June 07, this was dec06. i said ok.
In jan he said we could ttc and im now 26 weeks pg with our first dd. he is pleased and over the moon.
i think sometimes men dont realise HOW important this is to us.
I would recomend stating how this feels to you, and you listening to him. then, set a date at whih you will talk again, say 6 months. do not mention it in between.
explain you could work PT after baby, you will get Maternity pay if you are working already, and i know not to rely on this but you will get more CB and TC.
our car is just a normal car and fits 3 car seats, you will have to check that, even if you pretend at halfords that you want to buy one just to check the fitting.
i too am one of 3, dp is an only. 3 feels right to me too, and i always shared a room with my sister. we only have 2 bedrooms here but i know we will be ok, im not going to not have a baby becuase she may have to share a room for the first year of her life.
Please ask me anything more you want to know, i know how devastated and upset you must be.