Collect the certain number of blueprints to unlock the reward.
Accept Gimme the Money mission, its unlocked right after you meet with each faction for the first time, at the Mafia HQ. Now you can either cancel the contract and recieve the helicopter tight on the roof of the Mafia HQ or complete the mission and return the helicopter but as soon as you exit the helicopter jump straight back in so the mission finishes but you still have the helicopter
This is a 100% glitch that works everytime. All you have to do is, select something from the buy that you want, throw the grenade and just before the grenade hits the ground quickly go back to the shop select and choose anything else and select it. Then when you get back into the game with the new selected item the old one will be droped free of charge!
At any time during the game when you have a vehicle that needs repairing or more ammo you can get both for free by doing a mission and canceling the contract. All you need to do is park the vehicle in the base where the mission is, accept the contract, and then cancel the contract. You’ll get the retry screen, select no, and then your vehicle is fully repaired and rearmed without losing money. You can then do the same mission at a later time.