$1 product store,and limite purchase quantity

[qingtianyu9]

I have a shopping store and a $1 product store,when shopper buy more than $100 in my shopping store ,he can purchase 1 product in my $1 product store,For example:
1) Buy more than $100 in my shopping store , limite 1 product in $1 product store;
2) Buy more than $200 in my shopping store , limite 2 product in $1 product store;
3) Buy more than $300 in my shopping store , limite 3 product in $1 product store;
3) Buy more than $400 in my shopping store , limite 4 product in $1 product store;
3) Buy more than $500 in my shopping store , limite 5 product in $1 product store;
......

how to do?

anyone help me.