Well considering the Nexus 4 wasn't even available for sale on Amazon until a few months ago, your chances are slim. Plus on amazon it's individual sellers with large markups. You could try eBay, but again, there might be mark ups.
The best option right now is to go to Sprint when they have it on November 8th, and ask if they can sell you one off contract, and if it's GSM unlocked or not. Otherwise, T-Mobile will have it unlocked off contract also, but there's no pricing or release date as of right now. T-Mobile does have a email sign up for alerts when it's available.
Keep an eye on the Play store the next few days too. There's small chance more will come in stock, but most likely they'll sell out within minutes.