Cheapest 'live rock'. . .
There's a place in North Hollywood called Aquarium Works that seems to have way cheap prices. I think they may ship via container. . . with rock arriving 'dead' or nearly so. . . then spend time in a tank to revivify it. . . so mixing with some 'fresher' live rock might be necessary. . . but with the amount of LR you're looking to buy, it might work out real well. I haven't got their phone number, but they're on Burbank Blvd. Good luck. . .
Chuck