Did you buy a 16GB Nexus 7 from Google Play right before the price drop? You’re in luck, as Google has a price protection policy. If you purchased the device 15 days before the price drop, you are eligible for full refund of the price difference (in this case, $50). However, you’ll have to act fast, as these price protection requests have to be done within 15 days of the price change.
ASUS is doing something similar, but arguably less effective. Instead of refunding the price difference, they are giving €30 or ₤25 (in the UK) back in the form of store credit (as in, you can only use it on the ASUS Shop online store). So if you’re in Europe, you also have that option available to you. Hit the source links for both refund options.