Meat rabbit tractor

If I get rabbits and build a rabbit tractor and put the rabbits in it and put them in the yard, and move them every day, would I have to feed them anything else beside all the grass they are getting to eat?

Even with moving every day, I would still offer pellets. You'd be surprised how quickly a rabbit will chow down the grass they're on, and it's better to be safe and offer them a balanced meal with the grass, than risk problems.

What if I fed them hay, so they are getting hay and grass all day, I just don't wanna give them pellets, I'm tying to keep the cost very low

Understandable, but a large bag of rabbit pellets from a local feed store isn't going to cost that much. I get a 55lb bag for $15 and with about two dozen rabbits I go through a bag every week or two depending how many and what age my kits are at and that's with hay and grass being the supplements rather than the staple. If you're set against the pellets, then I would definitely offer them free fed hay and a mineral block.
Keep in mind also that rabbits don't always get along, so you'll have to be prepared to separate them if you're going to have more than one

yes i am planning on keeping the male and female seperated until spring, then let them mate and putting all the kits in a rabbit tractor, then in 10 weeks or so, slaughter them and during the winter keep a male and a female in my chicken coop in a pen and feed them hay and maybe pellets and when spring comes around start over

There are people who raise rabbits in tractors, but I believe they move them a lot more often than once a day (like, 3 to 4 times per day). Some of the hay you put in a tractor is going to get peed and pooped on, so you'll need to remove it when you put fresh in, or things will get really nasty in a hurry. You may find you are spending in time what you are saving in money, but if you have plenty of that, it works out.

A grass/hay only diet (plus mineral block) may or may not meet all of the rabbit's nutritional needs, and it certainly won't be as nutrient dense as a diet comprised mostly of pellets. You will probably find that it takes you in the neighborhood of 14 weeks to get rabbits to slaughter weight. A doe that is eating only grass or hay can't work as hard as one that is on pellets, so you will need to scale back the number of expected litters per year. Rabbits tend to lose vigor if you breed too close for too long; while you might get away with breeding a pair of full siblings for one generation, I wouldn't take it further than that.

What you are thinking about is doable, but you need to do your research. Check on BYH - I know of at least one person there that has done this.