Sorry, the government $40 coupon program has been over for many months. The "coupons" were actually like pre-paid debit cards that expired 90 days after issue. If you should happen to have one, or if you find one of these coupons for sale on Craigslist or Ebay, they have expired and they are worthless.
That being said, you still have a number of options:
Try your local Thrift Store: people often give them to charity when they no longer need converter boxes. Garage sales are also a good source, as people upgrade their old TVs. Sometimes they will be missing their remote control unit, but you can buy a replacement for about $10. Craigslist dot org is a good source, or you can try Ebay using our Auction-bot link at the bottom of this Forum page.
If you are near the Canadian or Mexican border and currently receive analog signals from foreign stations, or if you have been receiving a LP analog translator, the Converter Box needs to have a function called "analog pass thru" for it to be able to receive those stations. As an example, the Channel Master CM-7000 does not have this feature. Many Canadian and Mexican stations are now converting to digital or they will in the near future.