Since your bike has a 135mm rear hub, I'd go with a low end Shimano mountain bike crankset with external bottom bracket. You won't have any chainline issues and external bb are very easy to service. If you go with a square taper bb and crankset there's always the chance the chainline isn't right, take care to choose the two correctly.

there's quite a few options on ebay, usually out-of-box or takeoffs can be had for cheap