[Plugin WooCommerce] supplementary charges

Can you describe how best to add a standard supplementary charge to a product.

For example: I want to charge $100 per week for accommodation. I want to add to each order (irrespective of length of stay) a charge of $30 for admin.

Complicating factors: this is already taking advantage of a variation because each client needs to decide how long they will stay. In addition, there are several types of admin charge depending on the person (single/twin), payment type etc etc.