Check Gubroker, there is usually a few barreled Mosin actions up for sale at any given time, often for under $40
Or as an alternative-- Buy a complete one for $80 from JG sales or the like and sell off all the extra parts you don't need (stock can go for $40, Bolt $30, trigger and misc parts another $20, meaning you get the barreled action for free (or at least a low price once you figure in shipping and FFL transfer fee).