>>98518914They got 30k in the Kickstarter if I remember and you can negotiate with voice actors' agents if you register your product through SAG (Most VAs are part of it) and tell them the situation of your film and the budget of it, plus what you plan to do with it.
I contacted Richard Horvitz to do my student film a few years back and he had to deny it because I never registered it through SAG by the time I started production, but his agent was completely open to it, worked out what kind of price I should expect if I was able to get it registered (Around a thousand or over), and was even willing to ask if he would be interested if I couldn't get it officially registered. That was for a couple of minutes of animation.
If VAs have their agent information available online and you have a decent enough budget, you can get professional VAs no problem for your projects. The people making this short are in the industry though, so they're probably able to get their agent's information on a more personal level.
