There is a place in St Tropez which does it - do a search on the forum it was discussed before but I can't remember the name of the company anymore. Had a selection of med style RIBs of about 6 to 8 m and I seem to remember rates were abbout E250 to 300. you need a copy of your RYA L2 PB. They are based a coupld of hundred yards down from the marina.
It's called Marine services in St Tropez, they rent out Stylmers and Joker boats from 6.4m to about 10m i think. There were some Capelli Tempests up 4 rent in Antibes port, round in front of the entrance to the town.