Please don't ever purchase a Jack Russell Terrier from a Pet Store, because they are bred and raised in horrible conditions in despicable Puppy Mills. Check out: http://www.stoppuppymills.org/ or the Humane Soceity explanation about Puppy Mills: Get the Facts on Puppy Mills

If you would like a nice Jack Russell Companion, you should adopt one from Rescue. There are many many rescue organizations nationwide. I will provide links to some of the prominent ones below. You could also go down to your local Humane Society or animal shelter and adopt an available dog there that may be facing termination.