There are several flights a day from Bishkek and back. It costs from 30 to 50 euro.
There are two weekly sleeper buses (Mon and Fri) from [Kashgar] in China leaving at 10:00 (Beijing time) and the trip takes about 18 hours. The price is 470 RMB and the buses depart from Kahsgar international bus station. As the road through Irkeshtam is at high altitude, remember to take warm clothes to the bus even during summer. Sit on the left for better views.
Prices of shared taxis from Bishkek to Osh vary quite a lot. In spring, when seasonal workers are travelling from Osh to capital and then to Kazakhstan or Russia, it will cost less, and vice versa in autumn. Normally it can be from 600 to 1200 per car. In September it was possible to go from Bishkek to Osh by 7 places taxi and it cost 1100 som per car. Highly recommended road!
Colourful bazaar, open 7/7, biggest on Sundays, smallest on Mondays.