Well, I don't know about dental dams, but I read that Saran wrap can be used in place of a dental dam, I suppose also to cut the costs as well. Only problem I would guess is that it sticks together very easily. That's as close to a specific dental dam that I know of, but there are other options such as cutting off the tip of a condom and then cutting it up the shaft towards where the tip had been, and also using a nonlatex glove by cutting off the fingers and up the side of the palm. Tongue can go into the thumb spot of the glove. I only read about the last two but I think the condom one would be the best bet, and there are non-latex gloves out there for the other. Flavored lube may help out with the taste on the condoms, but I'm not sure if there are flavored non-latex ones. It may also help to look on online for other alternatives as well. I hope this helped some!
I haven't tried these but I have read about them, again online is a good source for other options and as double checks for these as well to. These might not be specific dental dams, but they probably are things that you have around your house or apartment.