Since Grubhub is only a platform that enables you to order food from restaurants or other places, they can not offer monthly or weekly packages, it is only a one-time delivery system.
However, Grubhub does offer a monthly subscription system that enables you to have free delivery on all of the orders you put in no matter whether the restaurant charges a fee on delivery or not.
But, this only works if you make an order of 12$ or above, that is the minimum limit to get free delivery on their monthly subscription service.