The Fish and Egg listing for the AKA is here:
http://www.aka.org/UserFiles/File/felpdfs/currAKAFEL.pdf
Ruth Warner on the list is good to buy from. Most of her fish are $8 a pair, and shipping is $8 for the first pair, and $0.50 for each additional.
Joe Scanlan has fish for $6 a pair, and he offers a discount to new AKA members.
Fred Behrman has some Nothos for $5 a pair.
All the above are on the F&E listing. I think you will find that shipping is a lot cheaper from experienced killie breeders than from the online auction sellers.
I would suggest getting at least two pair of a given species. If you're not interested in breeding them, you might be able to get all males at a lower price- sometimes breeders end up with extra males.
If you don't have a live food culture going (like fruitflies) ask the seller which fish will eat flake or frozen food. They might be willing to throw a starter culture in the box for a newbie.
The petsmart killies, while usually healthy, have to be the least colorful killifish I've seen. I'm not sure if they would look better when they got home or not.
You can also get Lucania goodei for free or nearly for free at Pet Supplies Plus stores sometimes. They come in with Ghost Shrimp and there isn't a SKU# for them. If the employees are in a good mood they will give you a bag of them, or throw a bunch into a bag of ghost shrimp. Sailfin mollies, flag killies, and other Florida fish show up the same way.
http://www.millevolte.com/nativefish05.html
http://filaman.ifm-geomar.de/Summary/SpeciesSummary.php?id=3211
There are probably some native killifish hiding in ditches and streams near you too. You might be able to find some at a bait shop, if you look up which fish are likely to be in the area. The bait people might know the fish by a different name.
Yes, you will be crossing the line from a mildly socially unacceptable hobby into the inner circle of the secret killie cabal by getting some from a breeder. Soon you will have a pile of 2-1/2 gallon tanks, and wondering what fish you can keep in a huge 10-gallon tank.