Wtd. (possibly) single speed conversion thingamabobs

[mountainloz]

i'm thinking of going single speed on one of my bikes, does anyone have what i will need to convert?
cassette adapter with ring and a tensioner?
just enquiring about prices
thanks

 

[jnrwookster]

I have a rear wheel built up with the single cassette/screw on freehub if it's any use?