Sorry, the government $40 coupon program has been over for two years. 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. Make sure to test them (if possible) before you buy a used converter box. Take a look at our Auction-bot link at the bottom of the Forum page: you may find a unit you can use. Another option is to replace your current TV with a new HDTV, which will both get you free broadcast TV and give it to you in High Definition. The cost for all sizes continues to drop and it is a buyer's market.
Make certain you have a proper antenna for it and be aware, rabbit ears usually don't work very well. We can help you select the right antenna for your location. If you have more questions, please ask.