My son wants some airsoft accessories for Christmas. I am clueless when it comes to this type of stuff. He has the G&G M4 Carbine Special Editions M16 Combat Machine Airsoft AEG Rifle (Black) He has mentioned wanting: * A rail system to attach accessories (He showed me a quad rail but I am not sure it will work based on where the battery is located) * A scope/red dot green dot sight * A bipod (He has a box mag on the gun if that makes a difference) If you know of any inexpensive upgrades for this gun that would greatly improve it, feel free to share. Please post links for your recommendations. We would like quality equipment but money is defintely an issue this year. I would prefer not to spend more than $50 per item (less is better). Thanks in advance for helping me figure this out.