Nylon will have better barrier but is more expensive. OPP will have less barrier but is cheaper. Both of these films would need a sealant layer unless you are just wrapping the product with a sheet.
LDPE would be the least expensive of the three and will seal but has the lowest barrier. Would be OK if you only need a dust cover for your product.
You will need to use a grade of film that has FDA compliance for direct food contact. You would not be able to use an industrial grade of film if the supplier states that it is not to be used for food contact.