My guess is as follows:
Directly behind the main speakers, vertically, on a hook. You'll have to move the movie poster, most likely.
Just left of the left speaker, below the thermostat.
Perhaps another behind your left side surround speaker.
Perhaps a 2pack of GIK 244, and 3pack of 242, totaling $320 before shipping. They also have (larger) room kits/combos, the smallest busting your budget by about $150 maybe.
If the 244/242, I'd use the 244s for directly behind the mains, and a 242 for below thermostat, another 242 for directly behind left surround, and the remaining 242 for somewhere else on that same wall.
Again, that's just my educated guess. Personally, I'd wait for b pape to chime in.
He may or may not mention the ceiling as a candidate.