Sopodo,
I trade through Mirus Futures. It works like this :
You can use Ninjatrader free, without a monthly charge, if you want to use the platform's basic functionality.
If you want to use its ATM Strategies, which are the platform's advanced features (automatic stop losses, indicators etc etc) then you have to pay the lease, or buy the licence for a lifetime.
The lease is $180 / 3 months. It is auto-renewing.
The lifetime license is $995 (I think). One off payment.
If you think you'll be using Ninjatrader for a long period (and want to use the advanced functionality) then it's a no brainer to pay for the lifetime license.
It seems there are brokers out there who charge you to use Ninjatrader on top of the lease / lifetime license ... but I can't comment on this , becasue I don't know whether that is the case or not.
I hope this helps,
Paulie