Increasing Payload by swapping out my Truck Bed

I am wondering if anyone knows (or can guestimate) the difference in weight of the old steel truck bed of the Ford Superduty compared to the new aluminum truck bed. I know on craigslist companies sell used truck bed bodies when they swap out with flatbeds/service bodies and you can get them for about $1500. Sounds like a nice mod one can do to increase their payload depending on the difference in weight. I contacted a guy on craigslist who ordered a bunch 2017 F250's and will be installing service beds on them and said he would sell me one. Is it enough to fuss about?