There were quite a lot of interesting points raised in a discussion. People suggested that using gibberish as a substitute for voices is a viable alternative, examples included Banjo-Kazooie and Animal Crossing. Others recommended using musical instruments used in games like Don't Starve. Both appear to have a long history in gaming. Not only are these solutions quick and easy, there's no cost to making them. So, it's perfect for my entry to an indie game jam.
Having trouble finding free recordings of gibberish, apparently it's a lot harder to create than you'd think, I made an attempt at the latter. I used music notes. I'm certainly no musician, so I simply opted to randomise the pitch and wait time between the notes. Changing the latter had a huge effect on the outcome. Short delays produced a very comical effect. Other suggestions are highly appreciated.
I tried a variety of different instruments. There are 6 in total. Some seemed to work better than others. I'll make my final decision after reading through feedback. Right now, the violin works the best. I believe I heard somewhere that the violin owes its popularity to being close to sounding like a human voice.
I wonder what other people think...