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?