Ramesh Lotey's wide-ranging, well-organised outfit organises tours and treks, rents motorbikes (per day ₹1000), changes money and is a good place for travel information generally.
A speciality is organising all-inclusive treks at relatively short notice, notably the eight-day Kibber–Tsomori (around ₹22,000 per person in a small group including donkeys, guide, food and equipment). The four-day Pin-Bawa route is cheaper (around ₹15,000 per person, three people minimum). The office is tucked into the [-shaped building that also contains more conspicuous Kuzum Spiti Inn. When it's closed in winter, Lotey remains in Spiti, so it's still worth calling.