What do you consider expensive? I am able to follow the keto diet on around $200 a month, and that's with splurging on things here and there. I've never really understood why people say it is so much more expensive.
After losing weight and maintaining the diet: it was more expensive to maintain a high caloric load after losing the weight. At the time I racked up about 6000 miles/yr on my road bike while at my optimal weight (no body fat to burn). Fats to supply the fuel I needed (mostly MCT's) were far more expensive than simple carbohydrates.
EDIT: I'm not complaining about the cost, I'm just comparing it to what unhealthy people are generally used to. I am currently on the Sated Keto (Ketolent) diet and it's costing around $270/mo which is perfectly acceptable.
When I eat candy/sugar/soda I can eat a lot throughout the day, and get a lot of calories in from sugar... i still eat smaller meals, but the sugar did me in. When I'm in keto, my appetite is non-existent, like ever. I'm hardly ever hungry. I don't produce ghrellin so most hunger is mental for me anyways.