You don't say which country you're in but here in the UK I'd just go round the nearest big supermarkets and buy all the stock on the shelves till I had enough - they tend to keep a fair bit in stock so you should be able to gather that 50 after about 5 shops unless you're unlucky.
Alternatively just order them directly from Tesco or ASDA and have them delivered.
Don't worry about taking a load of stuff through the checkout, 90% of the time the operator won't care what you've bought, just wants their next break to come and the more customers the faster the time passes, and if anyone does query just say "just stocking up a bit". As long as the payment goes through OK, they'll forget all about it as soon as you leave the till.
I've done 4 sessions with 50 cans now and I would always go to local grocery stores to buy them. In my area a can of Barbasol goes for anywhere between $1.30 and $1.60 a pop, so it's fairly affordable for me. I never tried ordering online but for the right price I'm sure it's a great idea and very convenient as well.
It's usually the shipping that kills you on something like this. I've gotten some good deals, like BOGO, from walgreens.com and drugstore.com in the past.