Vodka is most commonly used, to make vanilla extract. But Rum and Bourbon are also very popular, but add other spices to the extract.
Here in the Midwest, A good bottle of extract is about $7.00....2 vanilla beans from the spice section, of my grocer, costs, anywhere from $11.00 to $15.00. I have found, you can get good quality, cheap vanilla beans from Ebay stores. I have included Ebay links for my 3 favorite vanilla beans. This extract is of a superior quality, over the store bought kind, and you can taste the difference. I grew a vanilla orchid, once. It grew and grew, for about five years, I but never flowered. So I gave it away.
Ebay Source- for Madagascar bourbon vanilla beans
Ebay source for Tahitian vanilla beans
Ebay source for Mexican vanilla beans
3 vanilla beans
1 cup of your preferred alcohol
A small jar with a lid.
Split the beans, cut them to fit, if needed. The flavor comes from the seeds inside, scrape any loose seeds, into the jar. Add the vanilla and vodka, to the jar, and shake a few times. Steep in a dark place, for 1-6 months. Shake the bottle, once a week. I test it in a recipe, after 1 month. If it has a good, strong flavor, Then I strain, and bottle it. You can get a second bottle, by adding another cup of vodka, then steep it for about 3-6 months.