Yeah, you can use extract, but there's not much cost savings. Natural Vanilla Extract (not artificial) is not cheap. I would go to a place like Beanilla. Beanzilla? Something like that.
If we keep posting about VANILLA, the google advertisement for Beanzilla or Beanilla will pop up and you can just click on it. I bought 10 mexican vanilla beans from them and they were really nice. The cost wasn't too bad either...
Really, it's all about knowing where to get the stuff without getting gouged.
I took those 10 beans that I bought and put them into a 750mL bottle of vodka. It's about half-strength extract. Did you know that that is how extract is made? It's just vanilla beans soaked in vodka. The flavors tend to improve and meld with age up until about the 1 year mark. At that point, the flavor stabilizes and the product holds its qualities for years without notable diminishment of potency.
So I say buy 20 beans, soak them in cheap vodka. It'll be usable after a month or two. It'll get better for a year. Compare that to the cost of a real vanilla extract. You are waayyy ahead on money if you do it yourself.