MySQL User with Host set to a Range of IP Addresses
you can use the grant assign to a netmask like:

GRANT ALL PRIVILEGES ON database.* TO 'user'@'81.10.20.1/255.255.255.240';


It will give you access from 81.10.20.1 -> 81.10.20.14, just change the subnet part to fit the range you need.

You can see more info at mysql doc account names