Boyfriends 21st Birthday... Need Present Idea's!! Lot's of them!!?

Maybe you should take him on a picnic or something and then arrange that you go up in a hot air balloon or something. that way you get a cheap present as well as one you've bought and had to arrange. Am sure spending the day with you and the family will be enough. If he wants to go out that night, then go, arrange to meet mates etc. See what he wants to do but those things will be a nice start at least.