Installing gears is very difficult, and time consuming. Most people can't install them. I know how and can do it, and if I get to the point where I need new gears, I'll pay a shop to do it because it sucks that bad.
New gears are 350 per axle, give or take. Both axles get gears, so 600-700 for gears. The install takes me all day, so that's about 500 bucks labor. Look to spend $1000-1500 to get new ones.
I always suggest to folks to put the tires on. Drive it a month. Then if you don't like it, we can talk about gears. I go low as your axles will allow. 4.88 or 5.13 maybe?