The question is, when you are looking at MSRP price, what are you using to gauge a good asking price is? You can't just cut it down by 25% or something as they can tell you're not serious and haven't done your homework. Realistically, they're only going to come down so much. So what are you using to know what price to negotiate them with?
I don't see too much of a negative to negotiate the "what do you want to pay a month" when you also follow that up with "while leaving it an X-month loan". This will make them change their rates and trade-in values and cost of vehicle since that is all that is left. Do not leave it open for them to change rates and you can negotiate any way outside of that.
Also, on the lease cash option - I don't see any offers, at least where I am, where they are giving cash right now for Kia's. Don't they also require money due at time of lease? For example, right now on a Stinger lease, local dealer wants $4k due at signing.