well, in all fairness, the only time you won't get someone posting about the best value for money player would be if you start a thread entitiled "I want to waste my money and get a shitty stop gap player"
If you want to price up an xbox:
1x xbox unit (I buy em second hand)
1x replacement fan
1x remote
1x HD pack (Component wire
)
That's going to be about £50.
You'll also need a way of getting it modded, best way is get hold of a copy of one of the three games with network code vulnerabilities, and an official memory card (imo, hardest part of modding an xbox is tracking down these things).
So that's about £70, say, and you've got everything you need to mod any xbox into a HTPC setup.
These days, xbox is perfectly suited to SD content and DVDs, however for HD you must be looking at htpc devices.