Ryanair flights land at Sandefjord (Torp), which is about 110km from Oslo. If you're hiring a car, it's 470km (8h30mn) to Bergen, 375km (6h) to Eidfjord and 385km (6h30mn) to Sogndal, all 3 would be good bases to explore Fjord Norway, depending on what you want to see as well (eg Bergen, Hanseatic port with loads to see & do,
http://www.bergen-guide.com/ , Eidfjord is on the Hardanger and at the foot of the Hardangervidda,
http://www.hardangervidda.org/hne.htm and Sogndal is close to glacier country,
http://www.bre.museum.no/ ). In fjord country you can't go far without needing to ride a ferry - see
http://www.fjord1.no/en/ - Norway is very expensive, it's best not to convert Krone to pounds! When buying stuff, look for the word "tilbud", which roughly translates as special offer. If you like a drink, bear in mind you can only buy spirits & wine from the government stores, so you are well advised to take your own.