So $300 a month lease, no tack available.
What is the board bill currently?
Shoes and vet who is responsible for?
What are you allowed to do with the horse?
Jump, shows? Trails???
Or just lessons and supervised ride time in a ring?
I get paying a percentage, but not near the entire freight and load...you did say $400 or more right?
What happens if the horse gets hurt, goes lame and it wasn't you riding or created a problem?
How many others are going to lease the horse on your off days?
What is said and what is done are sometimes different to different people...
Although son is in HS, how much riding is he doing?
What kind of activities does he do with the horse cause it can make a difference, a pretty big one.
$800 for used tack is
You can buy a new saddle from a place like Dover Saddlery in their own line of leather saddles for not much more than that, NEW!
Check out Stateline Tack too for a nice selection of synthetic or leather saddles affordable and decent quality at affordable prices.
You can also buy used and get a heck of a saddle with all the fittings, bridle and such for less than that offer.
Craigslist local to you could be your best friend, so can many local trade publications and other places that sell used tack.
So many places at your fingertips with use of the internet and a look around.
Someone sees you being so wanting to ride and do they are setting you up to take advantage...
Innocently done, but they benefit and you lose a chunk of $$ from your pocket.