How long does papier mache last, I want to make art with it?

I have an idea for art pieces that I want to make, out of papier mache (cardboard and paper - using coffee filters and brown paper towel for the strips), actually I have already made five and they look pretty cool. It's like a 3 dimensional abstract painting of a cityscape and the buildings are made of rectangular prisms that stick out, they have lots of texture... hard to explain but I paint them in acrylics and they can hang on a wall, and you can put a bunch together to make a metropolis. Well the only problem is that they are papier mache, I just used recycled carboard box card and cereal box card so it is probably very acidic, my friend said I should sell them or put them in a gallery (she was only being nice lol) and one person I showed them to wanted to buy them, but I am worried that they are not high quality enough to be fine art because they are not made with archival quality materials which really I cannot afford. Do you think papier mache is okay for making art pieces with, that are considered art and not just crafts or folk art? If not can you suggest alternative materials I can use that will allow my little projects to last longer? Thanks.