WarpMyMind

I think there is a big difference in the amount of effort put into a file with a computer generated voice and a human voice. Yet seeing that a lot of tts files are offered for 25$ I think there should be a limit to what may be asked for them. I think 5$ should be max.
Of course if a lot of work is put into timing, echo's, background mucis, multi voices and more then a higher price is fine.

What is the general opinion?

I'm not one to place any restrictions on what files can be sold here or not, except for basic legality stuff. Don't know off the top of my head how EMG feels about that, but I think he's the one who's in charge of approving all sales. If people are willing to buy TTS files at $25, I doubt he or the author will complain.

In general, I think once you get past the most basic level of production, the script of a file matters more than how it's voiced. There are some types of files where the inhuman, artificial tones of your average TTS engine come in handy, but most scripts will probably work to some degree, even if a real voice can do them better.

There shouldn't be any limit, apart from the decisions of the author or EMG. As long as the file is clearly labelled as a TTS-voiced file, it shouldn't be a problem for anyone else either. Paranoid is right that TTS files are not necessarily inferior to human-voiced ones. Since you asked...
ZAP

I think they should be allowed at any price, though people are probably not willing to pay as much for a TTS file, so they should consider that when setting the price, that being said there are a few authors on here who have done well with the TTS files on here after getting a good reputation with free files. I do however believe that any TTS files should be clearly labeled as such so people know what they are getting before purchase.

I am very hesitant to buy a text-to-speech file. I could make my own script if I wanted to, and a text-to-speech generator just doesn't work all the time. The only TTS voice I can stand is Paul which is why I use him for my self-made files, and my friend enjoys writing up scripts so I use his from time to time. A human voice is easier to follow and has a unique pace, while TTS engines only have one way of saying things unless you massively edit the file. . . Which nobody ever does anyway.

In the end, I think TTS should have a cap of 10 dollars. It's absurd to pay anything around 20-30 for a TTS file because voice files, ones that require A LOT more effort, go for that price. No offense to those who make TTS files. It's like comparing a singer to a Vocaloid. The singers do a ton of work to actually turn words into song, while a Vocaloid is a synthesizer that takes 0% effort to "sing". The author of the songs, however, put in a lot of effort. It's just that they don't have the additional effort that the singer has to put in as well.

TTS files should be clearly labeled and if it's not labeled the buyers should be entitled to have their money back.