It all depends on your needs financially at this point. First off, you haggled (and it is a mostly forgotten art in the U.S.) and that in of itself leads in you in the right direction. If the price is right for you, then go for it. How familiar are you with leasing? One thing I've always known about it is that if you never plan on buying a car, it's a good way to go because everything about a lease is negotiable and and be carried over into the next lease. A factor many don't think about is where they are actually located. Leasing or buying a car on the east coast in New York City will be a different cost than some suburban community in the mid-west.
1. Did you haggle the capital price?
2. Did you haggle the money factor?
3. Did you research what old Prius's value hold at the end of leases?
If you answered yes to all 3 of these, and got them down to this price and it's affordable to you and you won't be handcuffed, or handcuffed very little, at the end with the final cost of the vehicle at the end of the lease when it is traded in, then you got a good price imo. It's been a while since I've dealt with leasing, so I can't really say what you got for sure.
The MSRP is about 24k, and from what you're telling me you're going to end up paying about 8K (not figuring interest). I see a lot of certified pre-owned Prius that are 3-4 years old going anywhere from 15-20k still. Meaning that they probably got them off the previous owner or leasee for about 10-15K. So as long as you stay under your mileage agreement, you should be alright with very little owed at the end, if anything.
I personally don't lease because I'm a "car guy" that can maintain a vehicle for many years, which is why I originally came to this thread I have considered it in the past though, but it doesn't fit my needs, but I'm not everybody either so good luck with whatever you decide.
Welcome to America.