As a stock music composer, you come across two types of markets where your music can be sold. The first decides the price for you, as in the case with AudioJungle, Luckstock, and many others. The second type allows the author to choose the price, such as Pond5 or Sellfy.
There has been a lot of discussion about the race to the bottom for music, and indeed the amount of people who search for "free music for youtube" or "free music download" far outnumber the people who search "cheap royalty free music" who far outnumber those who look for "high quality royalty-free music". With this, as well as new subscription-based stock sites being encouraged by youtube, it can really seem like us commercial music producers have hit troubled times. But all this gloom and doom goes nowhere, and the fact is that I'm a new player in the royalty-free music scene and I've been happy with my progress, so there's always room for new people and there's always people who will want new and interesting music!
A website that sets it's own prices, when done well as in the case of AudioJungle, sets the prices as they do for two reasons: the first is that they want a controlled and level ecosystem, a buyer can be sure that the great sounding track they find will reliably be a certain price. The second reason is to maximize their own profits as they choose prices that fit their clientele, presenting a boutique experience at a low price.
The sites that let you set your own price are looking for a different market and operate with a different plan. Pond5 may have less of the youtube and small business crown compared to AudioJungle, but their single-tier license covers broadcast use and is attractive to musical supervisors in TV, film, and games. With this in mind, the lower limit for music at pond5, $15, is absurdly low, and in fact could make your track look worse than it is, priced too cheap!
About a month ago I came across this thread on the Pond5 community forums.
After reading the comments, I gave it a try and increased my prices from $15-$30 before up to $25-$50 now. To my pleasant surprise, sales have decreased, quite the opposite, my sales are up, even on older tracks. Does this have to do with a perception of value? I'm not so sure, but I would encourage others not to price too low when they have the option!