Basically what wilykat is saying. Performance jobs are expensive because of the prep required for every single small job and because of the type of demands there is for these jobs. the shorter the job, the higher the expense per minute of delivery. If you want a lower rate you need to offer a longer gig.
There are not that many people who need top professional (voice) acting, but those who do are normally willing to pay going rates. Charging lower won’t make the actors get hired more because the amount of offers is pretty stable and most are willing to pay.
There’s also the factor of finality of delivery to consider. There are not that many really well trained professionals in creative fields (what outsiders consider really good many times is not really good enough), and they can allow to charge those rates also in part because their work is final and not fixable. That is, the product they are delivering can’t really be fixed post-hoc (maybe with some noise reducing filter and such, but the basic qualities of a voice performance are set on recording). So if you want a professional job for a product in which the quality of the acting might impact its success (the only reason to pay those rates, otherwise you don’t need a professional) you really don’t want to negotiate and go to less experienced actors unless you know really well what you are doing (including directing actors and doing your own prep as a hired, which is also expensive). Because if your alternative doesn’t work, and that’s very likely, you need to start from scratch again.
Finally there’s the recording and distribution aspect. @Timex, you know what’s the rate for Broadway actors having their play recorded and sold? (I’m curious, but I’m guessing that one’s a big bonus on their weekly pay)
Comparing something like this to software engineering or even to other artistic disciplines where the work is fixable and mutable (3D modelling, for example) is not very realistic.