Think we need a reply from the OP on storage size, a 1TB ssd would blow the entire budget
I am guessing on the A10 that audio processing will use similar maths to video encoding. There are benchmarks on that, where saving £80 on the A10 costs you about another 50% in time. If that is 0.2 seconds becomes 0.3 seconds, then meh. If that means 2 hours encoding becomes three, then that may or may not be acceptable. If that means only mixing 20 channels of audio together instead of 30 in real time, that could be game over. With a lack of practical experience here I think we need more questions.
Wooda, I presume you have a PC already doing this stuff? If so, what sort of spec is it and how good/bad is it? If we can get an idea of what needs improving and by roughly how much then we should be able to tailor this better to your needs.