I put a tablespoon of vanilla extract in my sweet black cherry jam, that makes 7 half-pints. Adjust your recipe for strawberry vanilla according to how many jars it makes. I stir it in after all the boiling and just before filling the jars.
BTW, I buy large quantities (30 or so) beans on E-bay for less than one dinky bean from a fancy gourmet store. I make my own extract with cheap vodka in quart jars (5 beans per). In 4 to 6 weeks you'll have good, dark extract. You can then add more vodka and use the same beans for more extract, maybe 3 times reuse.
Nancy

JR Mushrooms has good prices on vanilla beans too. I made Strawberry Vanilla Bean Jam a few weeks ago. Macerated the berries with just a tiny bit of sugar and whole vanilla beans overnight, then opened the beans and scraped the seeds into the jam. Followed Ball directions for low sugar jam from there using their pectin. Delicious!