Before the paved road the roads are often muddy, especially in the summer. There are no signs, but you may be able to get directions by asking for Kopan Gompa. You can take a taxi all the way up to Kopan. Ask for Kopan Gompa. From Boudhanath the cost should be around 250 rupees by day.
Night time is more expensive.
From Thamel, the cost is closer to 500 rupees. These are prices that should get you to Kopan with minimal hassle. You can negotiate with drivers for lower prices, but some will try to renegotiate after you enter the cab if the price is toward the lower. Taxis are plentiful in Kathmandu. Visa and Vaccination You will need a valid visa to enter Nepal.