http://www.charliethebikemonger.com/index.htm
if you have a chainring itl be good enough
its likely that the bolts will be too long as they were used to holding two rings and now only one . you could file the female part down , use spacers cut from an old chainring or buy new steel ones .
so far you havnt had to spend any money and you have some singlespeed specific cranks
next along is the chain , this depends on how gnarly you are , if you spend all your time seated spinning a small gear the geared chain you already have will work ( and will already be worn to your chainring ) i like 1/8 chains due to the width but 3/32 are fine
if you have to buy a new chain it will wear quicker unless you also change the chainring but isnt a big problem if you dont
so far you still havnt had to spend money unless you needed a new chain anyway and even then £10 will get you a good kmc that many people race bmx on
singlespeed chains wear quicker because you spend all your time in that one gear instead of spreading the wear across 8 or 9 other sprockets so be ready to change the chain more often
if you have a cassette hub go no lower than 16t , better quality steels are going to last longer , gusset seem to make the cheapest of the good ones and are about a fiver
£15 so far
you really should you a method to tension the chain , magic gears arnt exactly an engineering marvel and are best left to bikes that spend more time being photographed than ridden , the mrs bike uses an on one and it seems good enough , ive read mixed opinions about the dmr ones . they seem to be around £15 , any more and its just added fancyness , but they are available second hand for cheap
its best to have one that pushes the chain up rather than down and sprung is better than bolted in place
£30 so far
to space the sprocket you can be as inventive as your parts box allows
as long as the chain isnt going to touch anything you wedge on there its fine , mine has a few old sprockets and cassette spacers , avoid the kits that use two wide alloy bits , you need many thin things to get a perfect chainline . i wouldnt spend £10 on them though , go to the local shop and scounge a few old cassettes
i use a length of string to determine chainline , its easier to eyeball than having the chain in place
so thats the basics and it can be done for about £35 ( i added on a fiver for sourcing sprocket spacers of some kind ) if theres any specific part you want to know more about fire away and ill point you in the right direction with links and pics and stuff
