Taxi to Bern turns out to be unreasonably excessive (10)
I believe the answer is:
exorbitant
'unreasonably excessive' is the definition.
'exorbitant' can be an answer for 'excessive' (thesaurus). I am not certain of the 'unreasonably' bit.
'taxi to bern turns out' is the wordplay.
'turns out' is an anagram indicator.
'taxi'+'to'+'bern'='taxitobern'
'taxitobern' anagrammed gives 'EXORBITANT'.
'to be' acts as a link.
Can you help me to learn more?
(Other definitions for exorbitant that I've seen before include "Very dear" , "Exceeding the bounds of reason" , "High cost" , "going beyond the limits?" , "Unreasonable" .)