What are the cheap and reliable options for moving stuffs (say, 8 or 10 cartons of personal used items/books/some clothes) to Kathmandu from Boston? Time is no constraint. Please share your experience who have done this.  Thanks.

 take 'em all with you when you go back to Nepal. if you have friends/relatives going back, divide the items. 
but if i were you i'd sell the books (donate unsold ones), put good clothes for yourself and donate the rest. yahabata nepal saaman saarera ni sadhya hunchha? apartment sareko jasto ho ra? you'll be able to buy new items in nepal with the money you'll be spending to transport those old goods.