The only guarantee is to see a fertility specialist for gender selection. Even the most fertile couples are not guaranteed because you still half to go through the 'in vitro process'. As you get older (especially woman, the success of in vitro is lessened.)
Here is a part of an interview I found in regards to cost:
It’s a long, drawn-out procedure that doesn’t always result in pregnancy. And it’s expensive. It cost the Millers $18,480, just for the procedure. I am assuming US dollars.
Here is the link for more information:
Choose The Sex Of Your Baby, New Technology May Allow Couples To Design The Perfect Baby - CBS News
Don't bank on what Chinese astrology or any other 'wives tales' say. Which ever sperm finishes the race first is the sex of that child.
And another thing: If you are overcoming an alcohol problem and your marriage is rocky why would you want to bring another life into this world? It won't save your marriage.
I wish you all the best.