A great price for this would be around $150-$200 - here's why:
Price would obviously be dictated by quantity produced, but for arguments sake:
If MR can offer their FXs at $119 retail, and they're fabricated of die-cast, and injected molded parts, and include lights and sound, then this simple pistol would cost about the same, or less, if produced in the same numbers. It won't be, so it should cost more. It all has to do with 'minimums', which has to do with factory floor time, which has to do with job scheduling, blah blah blah...
What's important to understand is that each model produced requires "set up" costs to get into production - protoypes, die fabrication, and so forth. That's the hurdle each company has to leap to see profit (advertising goes in there, too). The price of the finished piece needs to incororate a little of that cost, but once the "set up" is paid for these types of toys are insanely cheap to produce - in China. FYI the FXs cost about $30 to make. The collector sabers that do nothing? Between $50 and $100 - because they make fewer than the FXs.
Example - it costs Sideshow $1,500 to make one of their lifesize T-800 endoskeletons. That includes shipping from China. They sell them for $5,950 thus making $4,450 dollars profit. Fair? If that's what people are willing to pay.
This should give you an idea of what this little pistol will cost to produce. Around $30. With that dandy moving trigger.
Sci-fi collectors have GOT to stop buying with their hearts, or at least declaring how they'd empty their wallets just to get their hands on that phaser they've always wanted. These companies play on your 'nostalgic love' of some show, or movie, and count on the fact that you'll "drop $500 on that in a heartbeat", and then pretend that their products are rare and exlcusive and mark them up 300% because the customers have already given them the go-ahead. All collector's markets are like this to some degree, but Si-Fi/Fantasy collectors seem to be particularly ready to part with their money for some reason. It's almost as bad as clothing/fashion - can you wrap your head around a 900% markup on a belt?
Demand a fair price and you'll get it, or suffer the alternatlive.
It's up to the consumer.