I only read this thread because I hadn't the foggiest idea what "lay away" meant. There is certainly something like what you describe here in LT, an outfit calling itself Distribuidora Acevedo S A , I don't know how big they are because we only ever see the same two fellahs. They come round every now and again with a big shoulder bag full of creams, potions, vitamin pills, shampoos, etc. You pick out what you want and they fill out a small card showing how much you owe,you get the goods straight away, our last purchase was a total of RD$550, We paid a deposit of RD$100, then they come round every Sunday morning and we pay them a bit more, last week it was RD$100 today it will be RD$150 but we don't have to wait until we've paid all before we get the goods. They seem to go to most of the households in our pueblocito. A few days after we've paid in full they'll be round again with their big bag.
A number of shops in town work the same system particularly for womens and kids clothes.