If you're a DIYer and handy, look for old galvanized trailers and refub them as needed and build out to fit what you want.
Galv trailers will work just fine for beach and really no one actually needs to back a kayak trailer into the water, even the wheels.
True, i'd rather have a new aluminum trailer, but it will cost you.
I've built out 3 diff kayak trailers over the years and enjoy the project. Current one I saw a galv boat trailer in a bunch of pieces in someone's back yard. I knocked on door and asked about it, the lady gave it to me for free if I'd come and haul it all away.
etrailer.com is a great source for all your trailer rebuild projects: https://www.etrailer.com/
Good tip below to corrosionX the leafs.