I just called Hatchmasters. They want $329 plus return shipping for a 20x20 hatch. That's for new plastic and seal.
You do NOT have to send the bottom frame of the hatch, only the hatch itself, with the handles left on.
I talked with Mark, sho was very helpful. We have 2 leaky hatches (leaky from the seal around the glass, not the metal-to-metal part). Since I don't need new lenses, only resealing, I might be able to use a new gasket (if they are Lewmars' Trimline or Coastline series hatches. Otherewise, the gasket is integral with the lens.
So he's willing to send me a gasket (and I'll need to clean all the old glue off carefully), or I have to send him the hatch top. Once I figure out which hatch series I have, I'll know more.
BTW, I'm not sure I want to drop $800 or more after tax on this. Would love to have another option. Looks like the PO tried using some black silicone or something to make the problem go away, but that isn't working, at least not now. I may have to bite the bullet and spend the $800.
These guys rebuild hatches complete with warranty:
Hatchmasters
I need to do the same but so far have not had much luck with gluing/sealing new lenses into the existing frames. The company in the link will do it, but they do need the entire hatch sent to them (top and bottom sections). I'm not quite ready to go that route yet.