As a lefty, almost every instrument I have purchased has been online. Make sure to buy from a place with a decent return policy. However, since you probably are a righty, you might consider whether it is worth making a drive to a music shop or two, even if it is a bit farther than you would normally go, so that you can put your hands on some five-string options. Even if you don't actually buy a bass from a shop, you'll at least get a better idea for how some different fivers feel, sound, play, etc. that might make a difference in what you choose to buy, and of course you could get lucky and find the right one in person.