Shangri-la to Dali (about 9 hours) and take bus at Xiaguan, Dali to Puer City. Buses are not hard to find. Ask in advance if the bus run to Puer city area. If not, you can get off halfway at Jinggu, which is about 3 hours from Puer.

The other optioin is to Kunming first from Shangri-La (over 12 hours) and then change to express bus to Puer (4 hours). The travel route of this line is most convenient to go like this: Shangri-La - Lijiang - Dali - Kunming - Puer.