I guess my first question is, how does Atkins end up being expensive for you? If anything, Atkins should be LESS expensive than the normal American pattern of eating a lot of processed food. By cutting out all of the junk food, processed food and sugary things (sodas etc) you should be spending way LESS money. You're buying fresh fruits and veggies, fresh meats and avoiding all the expensive name-brand expensive things on the shelves. You're drinking water instead of soda. Most people I know on low carb / Atkins end up saving tons of money on groceries ...?
But OK, back to the real question. First, are you sure you're really under 20g/day right now? It's very easy after a while of low carb to get used to the "general" maintenance stage of low carb that includes nuts, whole grains, sweet potatoes, etc. But when you are in induction you cut a lot of that out so that your body is in high fat burning mode. Take a look at this list -
http://www.bellaonline.com/articles/art16194.asp make sure you're not straying from that list.
Also, your metabolism may have slowed since you last did Atkins. All of us get slower and slower metabolisms as we age. So your body may need fewer calories to get through a day. Look at the portions you eat - are you sure you're stopping when you are full? Or are you clearing your plate "just because"? Try only serving yourself half a "normal" serving of each item when you eat. You can always go back for seconds, but you should never start out with a full plate. Going for seconds should be a normal part of eating, because it helps you be more aware of how much you really need to eat before you get full.
Finally, be sure you are drinking 8+ glasses of water a day, taking all your vitamins *including* essential oils. These are key to your body working properly and therefore losing weight.
If you do all of those things for two weeks and are still at a plateau, it is time to start adding a bit of exercise into the mix. If your body has little muscle in it, it has nothing that needs to burn calories. Muscles burn calories just by existing. So you need to maintain a healthy percentage of muscle in your system to burn the calories you feed it. Most people lose muscle every year as part of aging - so while you may feel you're exercising the same amount, you probably have less muscle now than you did back then. Meaning that you have to do something to develop it back again.
Let us know how you do!!