+1 for the newish Mac Mini - even a used one (2012 say) will only set you back about £300/£350 second hand. You can use generic memory to upgrade if necessary.
For me it's a no brainer. Mac wins hands down everytime due to the fact it is really plug and play, very rarely will anything go wrong. And if something does go wrong, you can just call apple and they will talk you through fixing it in a language you understand. Very few 'pros use PCs.
Even with modern PC's, there are just too many variables in the chain. Some people will get good results with them, but a lot of people will experience a lot of hair pulling.
(just to point out, i made my fortune (onto my second one now!) as a Microsoft centric software developer, I am a Microsoft Partner. Microsoft based systems are good for some things, but as a professional I wouldn't advocate them for music production).