Aimara are expensive, no way around that. $500 is about the cheapest I've ever seen them, but seems $800 is around average these days.
Some can be mixed in aggressive communities just like GATF, Armatus, or Dorado. Some say certain variants are less aggressive then others. I have an Amapa and has been fine with tanks mates so far from arrival at about 5-6" till now, maybe 13-14"? However, I've heard of one instance where an owner was hit when an Aimara shot out of the tank and bit his arm when it just crossed over the top of the tank. One like this might not mix well with tank mates.
The big difference that sets Aimara apart from most other fish is they are NOT afraid of people. When you clean or are in the tank for any reason they will attack. Very defensive of their space. Many fish may appear aggressive until you dive in then they shy away, Aimara confront, and the rage they posses can be pretty crazy if they're pushed that far.
I think most would agree if attempting to keep in a community setting it's likely best to get them as small as possible and raise with other fish.
I also know from a fellow keepers firsthand experience that large ones can test the integrity of the tank it's kept in. There was a monster out in Chicago and the owner said it would hit the side of the glass 180 so hard he was surprised the tank held up.
Aimara are kind of a spooky fish, the the way the almost raggedy fins move when they just sit there hovering- like they make the scary ghosts look like in the movies - the black of them that seems like just a pure absence of light, They just sit there hovering gills flared and staring right at you, you almost feel obligated to apologize and back away. They are a fish that command respect and seem capable of receiving it through intimidation in a single calm encounter. Hard to understand unless you stand in front of one, very easy to understand once you have.
My curupira wasn't scared of people either...at 3inches when I first bought him he nailed the guy at the lfs when he stuck his hand in to move a piece of driftwood, I was surprised he could draw that much blood at that size, but his personality has changed a lot since then.