The cost of Ross pistons and good metric rings will be over $600, so definitely not a "cheap" solution - but there are just not many "cheap solutions" for most of the components we use in high-performance flatheads these days.
I'd love to have a great hypereutectic piston supplier who would put metric ring packs on their pistons and give me custom bore sizes and compression heights - for a reasonable up-charge. I'd run these sorts of pistons on street engines - for many builds.