I read about making this on Ravelry of all places. It is intriguing 'cause good vanilla extract is expensive. Lots of people must be making this because a quick Google search yielded 2,520,000 results. I read a bunch, but this one from Instructables was my favorite.
I wish I could tell you that I slit a bunch of vanilla beans and tossed them into liquor bottles, but it is not quite that easy. First of all, vanilla beans are expensive. Wegman's (the best grocery store on Earth) charges $7 for 2 beans. I bought 6. I could have gotten them much cheaper on-line but I am impatient. Also, with Wegmans, I'm confident in what I am getting. You also need to sterilize the jars. An annoying, but necessary step.
The ratio everyone uses is 3 beans to a cup of vodka or rum. Supposedly as you use it, you can top off the jar and the beans will continue to flavor the extract for up to about 3 cups of booze. I did not know if we would like vodka or rum better, so I made a jar of each. They are hanging out in the kitchen pantry. In 6-8 weeks, I'll post about them and which we like better. I really hope that this stuff is as great as it is cracked up to be, because I have invested $39 so far. Now compared to $2.99 for 1 oz of McCormick vanilla, I'm doing great, but in the organic section, they have 4 oz for $6.99.
And, yes, I bought the cheapest booze I could find.