There is no feature currently available that will limit the maximum number of translations a user can create. You can however limit when a user will translate. For example:
ip nat inside source route-map NAT pool test overload
!
route-map NAT permit 10
match ip address 101
!
access-list 101 deny ip host 10.1.1.1 192.168.1.0 0.0.0.255
access-list 101 permit ip host 10.1.1.1 any