While A-6 is probably a good beginner's event, I think you're on a bit of a negativity trip. Limited (novice?) pennyplane isn't particularly hard to do, and ought to fly ok if it's a bit heavy. Maybe not QUITE as long, but long enough to be worthwhile.
The esoteric stuff you mention is nice, but not necessarily mandatory. I built a limited pennyplane using white glue, which was fine. I once built a 0.6 gram EZB. (At one time, that weight was competitive, but not when I built it.) Some of the best wood in it came from hobby stores. I selected it using a gram scale and a bit of testing at home. Perhaps the fancy glue bottle you refer to is very nice, but I find a plastic Luer Lock bottle with a tapered, fine pipette tip on it works nicely. The needle type are ok, too, as long as you never let the glue dry in the tube. You can also make a fairly thin nozzle by stretching a disposable pipette tip. These items will probably be mail order, but not expensive, and not necessarily from specialty suppliers either. For instance, you can get them from McMaster-Carr. However, for an A-6 or limited pennyplane I might just use a round toothpick and some Elmer's glue. The glue, if it's in the open, needs to be replaced every few minutes.
It was some time ago, but I weighed some of those plastic vegetable bags you find on rolls in the produce section of the supermarket. Weights varied, but the very lightest were much lighter than high quality Japanese tissue. I used some contact cement to apply it. The stuff is still FAR stronger than you need. On the other hand, something like Ultrafilm is much lighter and only about a dollar per square foot. Super Ultrafilm is even lighter, at about the same unit price. However, these two, and particularly Super Ultrafilm, are a bit finicky.
It's easy to make an A6 or a limited pennyplane at the nominal weight, though I'll admit I haven't tried one of the A-6 designs with the really long wings. I'm skeptical that they're really better, except possibly for high ceiling models that need to cope with a strong torque burst at the beginning.
The one item that I can't fake or by cheaply, that's very very useful for rubber models, is a rubber stripper. I haven't bothered to make my own, I suspect it would require a lot of fiddling, though I've seen some designs that are very simple. I bought a Harlan rubber stripper years ago. It's an elegant little machine, but I suppose it's only for the committed. (or the ready to be committed?)
If you want to be competitive in indoor events, the effort involved eclipses any building expenses. But the expenses are small compared to many other hobbies. They're also small compared to the travel and lodging required if you go to a bunch of contests.
BTW, I think wallpaper foam is a British or European item. I don't know how the weight compares, but you could use pieces cut from foam plates. There's even a contest for models made with them:
http://www.endlesslift.com/the-second-foam-plate-rubber-band-powered-airplane-contest-2017-2018/Kewl. That does say "beginner" to me far more than something built out of hand-selected super-light balsa purchased from specialty mail-order suppliers, glued together with hard-to-find glue thinned with volatile solvents dispensed out of expensive, hard-to-find containers, the covered with special super-light paper that is, once again, only obtainable from specialty mail-order suppliers.
What's "wallpaper foam"? Is that a US term? is it similar to 1mm Depron?
