I feel what everyone is saying about charging dude, because it's unlikely that you'll make a lot of money from this deal...but it really depends what you're trying to do.
If you like the way dude sounds and you WANT him on your beats, if it would motivate you to hear someone using your beats, then freebies here and there never hurts. You never know he could promote the shit out of it and it makes a little money that he then re-invests into music with you in the future...or he may have some friends who rap who want to use your beats and you can change them.
It really depends whether you want to be a "I'm not letting anyone use my beats, ever, unless they pay me" kinda producer or a "I charge those I don't want to work with, but am willing to work with people I like for free" kinda producer.
There's no harm in either method, just do you.
[color=#ff0000][i]3 x Beat Tags = Just $15
Voices Include Sexy American Female & British Female[/i][/color]