The best way would be to buy it yourself. Get a job!
You could try convincing them to buy it for you as a reward for doing well at school or do work around the house. They are more likely to go for it if the see you making a genuine effort
Good luck
start playing rec ball a lot to show you are keeping interested cuz it wount look good if you want to spend $100-$1000 on a Marker and your never play when you dont have a marker. another thing is be resposable. help around the house w/out being asked to show your responsable enuff 2 have a marker. and you should get a job too. the shows your reaponsable and that you want the marker so much u r willing 2 work your @$$ off 4 it. Good Luck!
Another good convincing aspect of paintball is that you'll be hanging out with good people and not getting into trouble. That and you not being around the house so much are solid points that parents really can't argue with at all.