funny farm is the other cheap hostel accommodation i know of. you can take private rooms and its not too expensive + 10-15 min walk to interlaken ost station.

interlaken is a good base as you are pretty much in the middle of everthing. a trip up the schilthorn/jungfrau is lovely on a clear day. you can check on the internet for web cam views i think to make sure you don't arrive up the top to clouds (it is quite expensive)!

the trummelbach falls in lauterbrunnen are supposed to be lovely also. there are stacks or walking opportunities near to interlaken. the harder is a solid 2 hour walk to top from interlaken ost but has beautiful views of both lakes. the beaternburg is beatuiful also for walking.

you will definately want more time than 2-3 days- its just beatiful here!