How hard is it to rejet a carb on 05 rubicon? Do you have to buy anything? Somebody told me that is a big job and cost a couple hundred bucks. Is this true?

 

What are you looking to correct?
Is it for going high altitude, or because you added a pipe and less restrictive air fliter?
If its bone stock, and you ride at 5000 feet or less, it should be good from the factory.
Jets are about 5 bucks each, no need to spend hundreds.

 

I am going for high altitude like 10000 feet. Where do buy them from and how big of a deal is it to change them?

 

This is gonna be kind of tricky.
Because the mixtures you need at 10k feet, is gonna be way too lean for lower elevations. Youre looking at changing the pilot jet, or maybe you can get by in just changing the mixture screw setting, and a main jet. But it wont be posible to have one setting on the carb, which will handle both areas.
You can change the mixture strenght by getting smaller jets(reducing fuel), or by opening up the air flow(increasing air). Either one ,will accomplish the same thing, and usually just increasing the air flow is much easier. Trying to change jets on the dusty trail is asking for problems.
Now if youre talking about bringing the quad up to 10 k feet, and leaving it there...then id rejet. But if you want to ride at both elevations in a day, then id play with the air .
Lots of guys put 1 inch holes in the air box lid, and at sea level they keep duct tape over them. As you gain altitude, and you notice the performance drop off, or the motor smokes black, or its bogging...start removing the duct tape which covers the holes. Going to 10k feet, you may need to totally remove the air cover, and strap it to the rack.
Just remember to put the air lid back on, and add tape as you decend. You dont want to run the motor in a lean setting.
Basicly, running too rich is only wasteing gas, running too lean can wreck a motor.