We decided to book a transfer from Nice to Monaco by helicopter as a surprise for our husband's 40ths. We didn't tell them until we arrived at Nice and they were blown away. The check in was fairly simple and you have to clear a mini security again, hop into a minibus to the helipad and then you are away (we had to wait 10-15 mins for our flight).
Once in the helicopter, the views are amazing and although only a short flight, well worth it. The cost was around £150 a person so not cheap - but definitely worth it as a treat for special occasion.