I can relate to a lot of what you are going through. My husband is in the service so we, too, do not have the luxury of having family close by to help out. Holidays are expensive considering JUST travel to visit each side of the family, let alone presents, etc. We were blessed with 2 boys and also had the repeated conversations about should we? shouldn't we? regarding a 3rd. It was my husband who was most torn about wanting to have another. He kind of got his heart set on having his little girl, after the ultrasound tech told him it was a girl. Needless to say, the tech was wrong! :-) I was content with our 2 boys and was actually very apprehensive about a 3rd. When we moved here 2 years ago, I was unable to find work and became a stay-at-home mom for the first time - I have adjusted to it and am now enjoying the opportunity to spend more time with my kids. Financially, however, the adjustment was more difficult and made me much more apprehensive about taking on another baby. Not to mention my fears of having another boy and ending up with a 19 year old boy, a 17 year old boy, and a 13 year old boy ALL AT THE SAME TIME!!!!
What it came down to was that I did not want to be the one to take the possibility away from my husband. I didn't want him to some day resent the fact that he would never know if he could have had a little girl because I "put my foot down" and prevented him from the possibility. We were blessed with our beautiful little girl and feel so complete. There have been adjustments we didn't forsee, however, in adding a third child...
We had to upgrade our vehicle to get something to accomdate 5 passengers. We had not planned on getting any new cars and had almost paid off one of them. Also, having a 3 bedroom home, we had to purchase bunk beds for the boys in order to put them in the same room. They love it so it hasn't been a problem, just an expense we would not have had if we hadn't added #3. And now that she is almost 2, she is eating all table foods and meals with us - it is amazing how much food we go through now! Casseroles that would feed us just fine before aren't enough. I think it is also a factor of the kids eating more meals at home, rather than at daycare, but good grief! the amount of milk and bread we go through in a week staggers the mind! I know with 2 boys it will only get worse but I hadn't anticipated the grocery bill to go up like it did quite this early in the game. Then there is back-to-school supplies, school clothes, additional travel costs with another kid, etc.
It has all been worth it to us but if my husband's income weren't fixed and guaranteed through the military (not to mention the excellent insurance coverage) we would be in a different situation. Good luck with your decision. Its a tough one.