Quick history lesson on licensed comm prop replicas:
MASTER REPLICAS makes a pretty spiffy comm replica for about $200 or so. They sell out and now go for $400+.
STAR TREK THE EXPERIENCE store sells a knock-off the the MR comm -- same features, but the fit and finish are not as "polished" -- but still, same sound features and spinning moire for a fraction of the price -- I think these retailed for $25 to $30 when they first came out. Some claimed they were made with same molds as MR, but I don't think this is 100% true.
DIAMOND SELECT comes out with comm replicas in the $30 price range that appear to be knock-offs of the STTE...but again, fit and finish not quite as nice...fewer metal parts. ENTERTAINMENT EARTH has an exclusive version with gold plated grid....others are flat gold painted metal. DIAMOND releases a later version with PLASTIC grid....but it has a crisper moire pattern than the first Diamond releases.
This covers out-of-the box ready-to-be-displayed-or-played replicas, not kits, like the HMS or jlong, as these have already been mentioned.
I think this info is more or less accurate -- but if someone else knows better, please post.