To get to other towns in the province you can take local buses or pick-up trucks. Inside Phonsavan, there are plenty of tuk-tuks, which might not be available without prior booking very early in the morning or late at night. A normal tour inside the town should cost about 10 000 kip.
There are 9 travel agents in Phonsavan that arrange bike, motorbike and car rentals. A bike costs depending on quality from 20 000 Kip per day. You can rent mostly scooters for about 100 000 kip. To rent a minivan costs about $50-80 US, but a four-wheel drive costs over $100 US. This includes or excludes gasoline, depending on the company. All prices vary hugely depending on season and availability.
Note that tuk-tuks are not allowed to take tourists to the Jar sites. You can visit the site with a certified guide or individually.