Thamel Area, Kathmandu
In a lot of shops you can buy this kind of art. Try to look carefuly, some artists are good some are not. It's difficult to get good information from a guide or someone else...
What to buy: Go for some self-painted stuff or an ancient work. Prices can differ a lot. I paid 75 USD for a really nice Kalachakra (50 x 50 cm).
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.