You'd have to price the cage yourself, based on where you live but do google, as some cages sold aren't actually suitable at all for Rats and can be dangerous.
They do have a littler tray
Apparently they are very playful, go figure. So, don't purchase small bowls for their food and water, they will tip them over. Get feeding "bottles" that attach to the cage.
Rats also like fresh veg and fruit, sunflower seeds but they need all the nutrition so add veg and fruit..
Toys? Don't know though I've seen many a mice show that shows wheels that they can run up and down.
The main expenditure is going to be the cage and set up, they like to be warm and nest as well, I've "read" that newspaper is ok and obviously cheaper, I read also not to purchase a pine or cedar cage, it's toxic.
With the litter tray make it big enough for them to get into but not too large it can be anything you want and ensure you empty it daily or else they won't use it and therefore, you'll be cleaning up a full cage every day of your life bahahaha wouldn't that be horrible?
You know there is a huge responsibility with any pet you own so do your research .
Food won't be expensive at all.. Start with the cage and feeding bottles, the rest will be cheap, ie) veg/fruit/newspaper/small plastic dish for the litter and litter..