Here is a free and good really basic low carb overview :
http://www.dietdoctor.com/lchf
Low carb is great, but it does not allow for much leeway - if you are someone who is going to frequently "cheat" you'd be better off on a different (low-calorie) plan - for low carb to be effective you need to consistently keep carbs very low, and you'll gain pounds (of water) each time you veer off course. So first, Know Thyself.
Second, if you have a "very very" slow metabolism you may well need fewer calories than any formula you find online would tell you. Any and all online guides are based on averages only - not on you as an individual. Some people can burn off all they can eat, and then some, and most of us who find our way to dieting websites like this one have metabolisms that would be really beneficial in case of a famine, because our bodies can eke out every last calorie from the food we eat plus convert some of it to extra energy (fat). As a woman over 40 who is not doing much exercise I can tell you that to lose I need to be well below the "recommended" numbers...
But my recommendation is to find a basic low carb plan and eat to satisfaction (not FULLNESS, just satisfaction) for a couple of weeks. During that time, count your carbs (many recommend keeping to 20g/day). After a few weeks your weight loss will likely slow down (that's normal) and then if it stalls for another few weeks you might need to investigate further (by posting a few days of menus here, for example, or tracking calories, etc).
Some ideas for lower-cost low carb foods - eggs are very inexpensive, most low carbers eat lots of them, cheaper cuts of meat for roasts or stews, can eat them for several days or freeze leftovers. You'll also save a ton of money if you don't buy any of the low-carb "convenience" and "replacement" products things like shakes, bars, candy ... those stall many people in weight loss anyway, and they will make your budget go way up. The basic foods of low carb - full fat dairy, eggs, meat, vegetables aren't all that expensive if you are only spending your food budget on that, since you'll no longer buy chips and cookies and ice creams...
Good luck!