Depends on where you find it. If I were lord and master of the Earth and determined to build the thing, my first stage would be to establish a base on the moon and set up materials production. The "lens" is a wire mesh, not a big hunk of plastic. Getting 50,000 tons into space is a matter of lifting 5000 10ton spools.
But I challenge you to suggest a cheaper way to get a probe to the nearest star. Again I said "most
" viable, not "super-easy-cheap-why-didn't-Columbus-just-bypass-America-and-go-to-Alpha-Proxima" viable.