Depends on the online store. AZgardens.com has a $25 minimum order...but aquariumplants.com does not.
My suggestion is find an onlien store that's reasonably close to you, so that you can use 2 day priority USPS mail, which is about 1/3 the cost of next day air. That'll work on plants only.
As for fish...if you're ordering $5 fish, then your
LFS should be able to order them in for you. I've bought stuff on liveaquaria.com because it was so much cheaper to get an invert pack plus some $20 corals, vs. paying $50 for the same corals at my
LFS. That made it worth the $22 for next day delivery.