Forward planning is the key to reducing your household grocery bills with bulk buying. It can be done, even if you can't afford the mega purchase right now.
The first step is research. Look at your shopping receipts and work out which items to target. What will you always buy, because it's either a necessity or a family favorite? What purchases rack up the costs?
Then remove the perishable goods from that list. They can't sit in a cupboard or garage for weeks on end. Look for things with a long shelf-life, which you consume in reasonably high quantities, and are likely to do so for the foreseeable future.
The next step is to research your items. Are there bulk versions of them available for purchase? If so, divide the portions by the price-tag. Do they actually represent real savings, when compared to buying the smaller quantities?
Order your items by the potential savings to be made. Cross off those which offer no benefit to bulk buying. The remainder will serve as your wish-list and a blueprint for the forward planning.
The third step is to estimate how much storage room will be needed for your favored bulk bought item. If you have the room already for it, then great! If not, can you rearrange things to get it in?
You could be downright cunning about this. Use the opportunity to have a clear out. You could have a yard sale or hit eBay with all that you're about to throw out. The best scenario of all would be if your decluttering raised the necessary funds, which will pay for the industrial sized household goods taking their place!
But if that didn't happen, then you're onto the fourth and final step. This is to put aside anything that you can afford, week by week, with a view to eventually buying your bulk item.
There's really no rush here. Your family are always going to consume those goods, so it's largely academic whether you've bought the big version this week or six months down the line.
That's forward planning. That's the goal. Your dollar a week put away now will grow. It represents mega savings in the future, once you can access the bulk buying market.