MTB wheels can't cope with trials.
http://www.tartybikes.co.uk/135mm_fixed_hubs/trialtech_race_sealed_rear_hub/c21p11423.html
http://www.tartybikes.co.uk/complete_freewheels/tensile_60_click/c16p398.html
Those two together will do the job perfectly. Slightly cheaper than a hope pro II, and leaves you open to swapping to front freewheel in the future.
Seeing as your current wheel sounds f**ked, it might be worth opening it to see if there's anything you can do. Remove the cassette. Try pulling the freehub body - that's the bit the cassette sits on - out, and anti-clockwise. You have to pull quite firmly. If it doesn't show signs of moving, there might be a nut or something to take off that'll be on the end of the axle.
Open it, if there's tiny chunks of metal lying about that's why it's bust. Take a pic and post it up, perhaps.