I'm looking for subscription management store to host along-side our current system. Where customers can sign up for different services, each with many "tools" underneath them.

These services and tools would all have start-up fees and/or monthly fees. The monthly fees should stack per customer so that they would only have one lump payment every month (very important), based on what products they are "subscribed" for.

When you buy the product, all that needs to happen is a flip of a switch in our database.

I'm looking for a solution that will require the least amount of extra development.

Does anyone have any suggestions for platforms/full-service sites that would be worth exploring? The closest thing I've found is aMember.com, but it would take a good amount of work to get both our and their systems to work together.

Much appreciated.