OK....First you need to tell us what size tires your ride is currently wearing. If you go wider, your aspect ratio will increase, thereby raising your Jeep by fractions of an inch for each increase in width.
For example if you currently have 255/75/17 tires, then you can go 265/75/17 and be 10mm wider. But wider tires mean more unsprung weight which gives a harsher ride, uses more fuel, and is tougher on the suspension. That's why when people start upping their tire size to the big ones, they get suspension lifts and springs and shocks, etc. My Jeep has 255/75/17's on them and the ride is rougher than when I had the stock 225/75/16's on it. MPG has for the most part, remained the same....from a low of 15 on backroads (hunting) to 23mpg on the highway and main roads. I would guess that for each size you go up, you could expect to pay 100 to 125 dollars more for a set of 5 tires.