[Rich]

10M/s per second only gives you a maximum of 3200GB/month (really, more like 2250GB/month after overheads) and that is for constant traffic. It will be less if it is not always totally maxed out and also would be limiting downloads during the peaks.

I'd say he needs to think how the traffic might grow and how long he expects to keep doing this. I think your 10x prediction is more realistic than finding a bargain solution.

An option would be to offload the audio files to something like Amazon S3 and keep the existing hosting for the low traffic stuff. The cost will be about the same as a dedicated server but it should be simper to manage and should be able to cope with traffic spikes more easily.