What to buy:
Themel is full of small shops where you can find your souvernir of everything, silk, cashmere, musical instruments, crafts, books, Nepalese tea with beutiful bags, knives...
I personally like paper lamp cover very much. Negotiating the the price of 40Rs each, I bought a lot with different kinds of designs.
What to pay: 40Rs/each
For all your travel related information books, maps, route plan, wall posters try this shop. Prices are okey but you get quality stuffs.
What to buy: Travel related Maps, Books, Picture Post cards, etc.