The Nuna Pipa car seat is $100 off on mbeans.com bringing the price from $300 to $200. This is a popular car seat and has great reviews. Switch to the blackberry color to see the reduced price.
I understand the deal is probably too specific, but this is the best Ive seen on this car seat in over 6 months of looking. Usually you can't get more than 10% off. Also, no tax except in MA and CT. and free shipping.
Also, yes there are cheaper car seats. but if this is what you're looking for, its pretty much the best deal out there.