I used to do couponing as a hobby, and spending $75ish for over $300-400 worth of stuff was pretty normal for me. (Some areas are more coupon friendly than others, for example, around here there are not many stores that do double or triple coupon days, where you can really rack up the savings, especially utilizing specials and sales)
However--it does take time. Many times you'll need to buy or beg extra Sunday inserts (not a big deal if you make connections). I had a giant binder organizing the coupons so I could not have to hunt forever for them. It is a really good way to build up your prep stock, since most of the items are processed with a long shelf life.
To this day I NEVER pay for toothpaste or toothbrushes, even though I do not mega coupon anymore.
Mega couponing also means that you have to be patient and charming sometimes. I did my shopping on a very specific day where I knew the manager and a couple of the cashiers who were good (a lot of times though the manager would put his new people on me so they could be trained in on coupon use--which was nice because they wouldn't get huffy and would allow me to help them as well), and for politeness' sake I chose a time where I would not be holding up the line if there was a new/inexperienced person. (Because couponing is fairly rare, a lot of times cashiers don't know what to do, and if there is a line building up behind you they get frustrated. Be prepared for nasty comments from other shoppers too, if you do this during a rush). I also for courtesy made SURE that I had the correct coupons, organized properly, ready to go (had all the ones where the cashier must write in the price separate and asked if they wanted those first or last, ect.) I also separated out the stuff that did NOT have coupons attached and had the cashier put those in bags first, so that if we needed to fish through stuff if there was a scanning problem we knew were to find the items.
It can be a really fun hobby, though. When I finish up my preps pantry project and have assessed my inventory, I will likely take it up again--but ONLY for non- or not-as-much- perishables and toiletries and first aid supplies. I don't feed my family processed crap--and a lot of the foodstuffs available through couponing (junk cereals, ect.) that are the best deals are just not things that we've decided as parents to make part of our lives. (We buy 80 percent of our veggies from local farms, all of our meat/eggs/dairy/poultry from local people. Wintertime is really the only time I utliize the grocery store on a regular basis. But if you eat a lot of of the stuff anyway, it is great for majorly axing your food bill!
If you are totally new to this it MAY be worth the investment to join a website that gives out lists of loss leaders/specials/plus coupons that you can use on top of them so that you learn how to put that kind of thing together for yourself. You will find that most stores (and flyers/inserts) operate on a 6-8 week cycle--so you'll need to clip everything you want and save it for a couple of weeks before it's the right day to cash in. Just clipping every week and looking for coordinated sales that week may save you some money, but the real couponers need to save/store their coupons and spend awhile each week checking out the specials and what they have in ther box so they know what to use when at each store. It is complicated, but pretty fun, IMO.