In the UK if the bike will see any public road a brake of some kind other than your legs are a legal requirement for a fixie. Does not seem to be the case in the USA. They are great in the snow though and that is a smart bike
TA do a set of road cranks for square taper BB that come in 155-185mm lengths. They are the Carmina or Vega cranksets not cheap though and the Vega is the one designed for MTB use.
Id go down the local recycle centre and see what is around in the kids and bmx bikes. At one time chainsets were steel and had cotter pins and the rings never wore out but the cotter pins always found a way to fall out. A kiddie size chainset in steel would probably weigh the same as a standard size alloy chainset, just don't get one in pink unless thats your thing
further to the middleburn tip, the spider can be changed so you can fit a compact drive one and therefore a 32 chainring...fixed off road sounds like a laugh, i do find that if i have been on my fixed langster i have a job remembering that i can freewheel on the other bikes