Since people are born gay it would require you to compare homosexual and heterosexual DNA, most probably of a large sample size. Employing expensive equipment and skilled geneticists, then once you identify the "gay gene" you would have to then put forth even more money to successfully research and produce a "designer baby" set up to genetically edit the DNA of a fetus so that they aren't gay. But, if you think of it that way you haven't actually turned a gay person straight you just prevented a person from being straight before they were even a zygote. So that doesn't work, and even if it did count, I think we far exceeded the 1 billion dollar mark in overhead cost.

I suppose you could come up with a formula that suppresses the expression of the gene, and also artificially pump sex hormones into them to drive home the straight part rather than just make them a sexual if such a medication should exist. And that's only if homosexuality is simply hormone based and not, based upon brain structures or something like that. Which would make it even harder if not impossible. And that's not even considering the ethical implications, I assume that the person in the scenario is willing but still it reaches some pretty dark gray areas.

From the resounding failure of conversion therapy it pretty much would be safe to assume environmental and behavioral therapy doesn't work. Maybe you go into some weird hypnotherapy that causes them to perceive opposite sex people as same sex a long the lines of the movie "Shallow Hal." Then you get into technicalities that they are in fact still attracted to the same sex, they just see the opposite sex as the same.

Basically, it would require a massive portion of your life, a large portion of the money to even start off, and even then it would be an off chance. No deal.