I have just arrived in Fribourg and viewed an apartment that I like but with extras it could be just ove my budget. I know the apartment has been on the market for over 6 weeks now, so there cant be a lot of interest in it

Is it the done thing to negotiate the rent?

I do know someone who did this after an apartment was empty for a year, I suspect you wont get far,

Generally no. But it never hurts to try. I say go for it as long are you are to be rejected, if you get positive answer then you'll be happy.