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 3000 to 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 $US50-80, a four-wheel-drive costs over $100 US. Depending on the company the cost either includes or excludes petrol. All prices greatly vary 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.
Take a motor-bike, all of them are semi-automatic, so you do not need to be an experienced biker. You can visit all the three Jar sites even though sites 2 and 3 can get a little tricky if it rains. You may not go to few other places like War Spoon Village unless you have an expensive tour guide. Even if it is a a planned move by the tour companies, it still is fun to ride through the villages. Ask for a map at the renting place or your guest house.
You can also cycle to Jar Site 1 from Phonsavan. Depending which map you believe it's 8-15km away and although the roads have some inclines it's possible to cycle there without being especially fit approx 45 mins or less. It's easy to find - the junction off the main road is signposted and from that village it's 2.5km. Parking your bike at Jar Site 1 costs 2000 Kip on top of the entrance fee.