We only ever had 1 key for our GV1600,it was really showing its age and for a couple of years I have been mulling over what to do about it (don't want to rush these things LOL).
I had enquired with a couple of car locksmiths (neither of them very local) and they both quoted £300 (it is a 2 button remote key type).
At the suggestion of a garage owning near neighbour I contacted our local Suzuki Dealer who quoted £280 but because I managed to find the little metal tag which had the key number stamped on it (I had put it somewhere safe ) that gave me a £30 discount as suzuki then did not have to do a search for the key number.
We had the new key 2 days later and worked fine even though it had been cut 500 miles away,we had to pop the car up to the dealer for 15 mins for the remote to be programmed to the car.