What's the best way to do this....

We have 10-12 products and want to offer a TOTAL PACKAGE type deal

so, we create a product called "TOTAL PACKAGE" and it lists all our services. as I add each service to the invoice, the system adjusts the cost based on the total services added

so, I add TOTAL PACKAGE, the cost is $15,000

I then take off SERVICE 1 and it subtracts $3000

I add SERVICE 16 and it adds $2000

basically, how do I set everything up so that it calculates price of an overall product based on the services I add and take away?