You can ‘buy-it-now’ a 3 month Netflix code on Ebay for about $14-15.00. Auctions are going for less. Occasionally you can find the codes as promotional gifts too.
Here’s a search. I am not affiliated with these sellers in any way.
These codes give you 23.97 in value on your account. That’s like buying 2 months and getting 1 free, or about $9 in savings over 3 months.
The Chromecast codes are now widely reporting to be stacking and I just stacked the ones I had. I expect this will drive code values on eBay up.
(I’m just not sure how long they will let the stacking last.) That means you can use more than one code per account if you have them. A lot of people DO have them, because there was a special deal online and they got them free and they are coming on promos for the Chromecast device.