This is the first time I've heard of using foam board for shelf liners, so I'm not sure what you want your shelf liner to do for you.

Usually, I just put some shelf paper down, after cleaning the shelves. If you will only be there 6 months, do you even need shelf liner? Maybe just clean the shelves well, and use them? Then clean again before you leave.

Or pick up some shelf paper at Walmart or Target, cut it to size, and put it down on clean shelves. Then when you move out, just remove and give the shelves a once-over.

the house is from the 1950's, and I'm sure the cabinets are origional lol! So, something between my dishes and the cabinets. Even with cleaning, I don't know that it would "feel" clean to me. I want a softish surface between the two. I like that the foam doesn't get wrinkled/move once in place, and provides some give. I'm trying to think if there are cheaper alternatives.

Well, they make a non-slip shelf liner that has a slightly cushioned feel. Or you could just do the foam board again, but that seems like a lot of time and money and effort for 6 months.

If you are near Ikea they have 2 different versions, one is a heavy duty vinyl and the other is more plastic. They are less than the brands sold at the big box stores.