Poipet border crossing to Battambang. Buses depart throughout the day and tickets are $4 - $5. Best to buy a ticket at the bus companies office to avoid being scammed by a tout. Journey is about 2 and half hours. A seat in a taxi is $6 - journey 1 and half hours.
Paramount Angkor Express - tel 012 320 737 run a morning and afternoon service.
Best option is a taxi to Battambang $30 - a seat is about $6 - journey 1 hour 20 mins.
Paramount Angkor Express Bus, BtB to Pailin $4 7:30, 09:30, 10:30 and 13:30.
Buses from Siem Reap to Battambang and visa versa. There are many bus companies that run a service between these two cities.
A seat in a taxi is $6 - 2 and half hours.
A Taxi from Battambang to Pailin is $25 - a seat is about $5 - journey 1 hour, plus 20mins if going on to the Phsar Prum border crossing for Thailand. Battambang taxi stand for Pailin is at the south of town, see city map.