Here are some alternatives for transport to different places close to the Jotunheim area. You can get closer by connecting with local buses or hitchhike or something.
Try to use Googlemaps to see where these destinations are.
Bergen - Tyinkrysset with the øst-vest express cost 415 NOK, further connections are possible to Gjendesheim and Beitostølen.
Bergen - Sogndal (change to Skjolden with local bus) cost 412 NOK
Bergen - Årdal cost 410 NOK
It's fairly straightforward to catch buses from Bergen, they all leave from the central bus station. They always have room for everyone (they use two buses if needed I believe) in my experience.
The tourist information in Bergen is good and reliable, you can also visit the Bergen Turlag office (local branch of the Norwegian Trekking Association) at Tverrgaten 4-6 (street adress) in the center of Bergen. http://www.bergen-turlag.no/index.php?fo_id=2706
Free camping is easy up in the mountains, and paths are fairly well marked with red markers on trees or rocks as well as the path itself. Beware on long stretches of rocky surfaces were you'll only have the markers to guide you.
For information about hiking in Norway see especially "useful tips" and "faq" on this site:
http://www.turistforeningen.no/english/
You're in for some great trekking, but Jotunheimen is high altitude so remember to prepare for all kinds of weather even though it's summer. I don't know when you're going but late July and August is ideal for this area.
Have a nice trip!
