Free leases in my area aren't common (Or I've never seen/found one)
$250 a month seems really good, (even better if you could ride more)
I pay $280 a month, and can ride as much as I like, so I do.
But if you can pay $250, and not have the responsibility of having to go feed everyday, etc I would probably take it or at least try it for a month, then if you are really getting on and want to buy him, look at options to get him closer?
The other thing you could try, (Some owners will work with you, some may not)
But if you spoke the the owner and said you'd only be riding twice a week, good you perhaps get the price down to $200 or 'x' amount you'd be happy with.
I know my owner is happy to do that, if people aren't planning to ride or don't want a 'full lease' he will work out a price that suits what they're going to be doing.