it depends what you want. do you want a true free float handguard? or one that is two peice that replaces the factory plastic ones? if your looking at a true free float you will need a armors wrench, action block to remove the barrel nut as it replaces it. the big name is larue tactical and daniel defense for the free floats, as they are the lightest.expect to pay around 300 for one, YHM makes value priced free floats, for around 100, they are the rails you find on most factory guns, but they do have a tendancy to loosen up. if your looking for a two piece i think midwest industries makes decent ones, also daniel defense, they go in just like the plastic ones do with the delta ring assembly holding them on. or you can just get some small rail sectiosn that bolt on to the plastic handguard. dont be intimidated about the install, its pretty easy,. go to ar15.com to get a better idea.
companies like lauretactical.com. globaltactical.com, bravocompanyusa.com will have the stuff you will need. for good prices.
4 rail handguards do add weight unless you get a high end freefloat, so you need to think about whether its really worth it. i dont really hear anything good from first samco.