Sounds like the prices quoted are for larger parrots. Way up here in ND, juvie parrots sell for about seven to $15.
As stated in another post, they should be fine with the fish listed. Just remember, your parrot probably will act pretty weird when you first bring it home. I've hear quite a few stories and witnessed acclimating them. They're a little dodgy when first released. Do you know how big the parrot is? (the one you quoted prices on)
I think it partially depends on how long you've had the oscar. Better phrased, how long the oscar has been in the 100g. Also, what type of personality it has. the oscar might try to fend for territory when it sees the parrot for its a new tank mate.
There's only one for sure way of knowing. Get parrot and find out. I suggest a couple of caves or tunnels or something similar for it hide in when first introduced, like pvc. Something that's big enough for the parrot to hide in away from the oscar, just in case.
If it goes badly, you could always bring it back. if the store doesn't have a return policy of some kind in effect, I wouldn't even bother shopping there.
Good luck,
you should try to post some pics if all goes well
BobRoss
