Here's my 2 cents referring to the first post of this thread. I just printed a minigun replica on my own 3d printer.
http://www.therpf.com/f9/3d-printed-minigun-replica-186044/
Now, I'm not making these to sell. This was just a project that has been in the works for over 3 years. I spent many, many hours creating the CAD files for these parts, just as many hours as if someone had carved then by hand. But here's the thing.... There are parts in this gun model that would be almost impossible to cast. Look at the receiver and feeder/delinker housing. These would be nearly impossible to mold because of the complexity and thin walls, undercuts, overhangs, etc. In this case, 3d printing was the best option. Now, I know the topic has gone in all kinds of directions here, in this thread, but the main consideration is: How does the finished product look? Does it show printing lines? (mine does not) Does it look 3d printed? (mine does not, which is a good thing) Was it more efficient to 3d print the entire gun? Yes, plus it is symmetrical and the lines are sharp & clean as if was machined. At least for this type of prop (mechanical, guns, etc) 3d printing is much better in my opinion. More organic stuff? Well that could go either way.
Now.... I probably wouldn't charge any less than 3k for this gun if I had to do it all over again. I know the point of price and efficiency was the main concern. Well, It's all in the buyers hands. If the buyer likes what they see, if the prop looks clean, looks smooth, looks screen or real-life accurate, WHO CARES how much it costs to make. If the prop is dead on perfect, can't tell it from the screen used prop or from the real life object, then it is the buyers choice if they want to spend 3000.00 for it. If they don't. They will look for something less expensive. If they find the same prop for 300.00, that was hand made, molded, cast, etc. but isn't quite as clean or straight or whatever, that is their choice to go for the less expensive version. You really do get what you pay for.
Now, I don't make props for a living so I can't speak from that vantage point so efficiency is not my priority, but quality and the satisfaction that I did the best job I could, is.
So....it doesn't matter how much someone is charging for their prop. If it's too high, get it somewhere else. If it's too high because the overhead was too high, well..... Is it worth it? Does it fulfill your expectations? If it's mediocre, look somewhere else. If there is nothing out there that even comes close to it in detail or accuracy, then I guess the buyer has to choose how much they are willing to spend. For example, there are 2 similar props in quality, one 3d printed, one cast. If 3d printed version is more expensive, the buyer will chose the less expensive cast version of course. The seller of the 3d printed version will lose the sale and learn their lesson. Maybe find a more efficient way to approach it next time.
I think it's ridiculous to put down 3d printing! Sure, there is crap out there, badly finished 3d prints with print lines, whatever! But there is also the same lack of quality with some of the traditional prop makers out there as well, crappy molds, crappy finishing, etc.
No matter how a prop is made, The price should match the quality of the finished product no matter how it was created because I guarantee you, if it looks phenomenal, then there was a LOT of work put into it - not just "save, print" !