hey, i feel for you.
when i was 3 i started riding, i'm now 14.
my parents said the only way i can get a horse is if i support the horse my self (everything...tack, initial cost, all the bills...) they'd only help if it was absolutely crutial.
i lease, and have been leasing since i was 6. i try and work out deals with the owners so that i can work off my lease. right now i lease two horses, and get to ride them whenever i want in exchange for 3 days of barn work and paying for farrier bills for one horse. also, through that lease i've worked out to ride for a lady in a neighboring town.
imo, it's all about finding the right deal. i've been in a situation where they've asked $500/month for the lease..and by showing them how dedicated i am, and how trustable i am, they let me work out the lease. you may want to find a place that leases out horses..and start riding there, taking lessons and stuff, and eventually start doing barn chores. then, once they realize you're trustable, a hard worker, dedicated, etc. they may let you work off a lease.
where do you live?