Scott:
When I owned a Seabird 37 (Sail) I added a swimgrid. It was a great addition. Many of the SB 37s added swimgrids, as it seemed the right thing to do. Many different appearances, Teak, Stainless box tubing, Plywood, Fibreglass. Mine was Fibreglass. I designed it and had it fabricated, as a class project when my brother was teaching plastics at a high school. It only cost me for materials, so was quite cheap. I put several grab holes along the stern of its perimeter, which were handy when swimming, and to which the dinghy painter could attach. The supports were Stainless flat bar with Stainless tubing on the long side of the triangle. Those likely cost as much as the FG. Long time ago so I don't recall the numbers.
Mark:
Your boat looks too good to go with anything less than what it should have had when it was new, TEAK! It won't matter in a couple of years that you had to pay an extra $500 for materials, just to get the best. Try wholesale hardwood places. You are going to be buying enough that they will talk to you.
When I redid my swimstep, I bought two teak boards. First I measured what I would need of 14 ft stock, that was the first board. then I measured what I would need in 2 or 3 ft stock, for between the openings, that was the second board, and because I didn't need a 14 ft length for this, it was less costly per bd ft. Mine was for a 13" extension of the old swimgrid, so was about $500 (at the time, 2007 IIRC).
The bronze supports also needed to be replaced, as one was cracked and all were designed for a 21" swimgrid. The new Stainless supports were about $1000.
I was able to re-use the old teak swimgrid, by flipping it over and cleaning it up, so with the new boards attached on the side against the transom, it all looked new. now that it has aged gracefully, all is silver coloured and no-one knows where the new ends and the old begins. I also had my swim ladder lengthened so it would flip down over the edge and flip up to rest against the transom, just like before.
Before and after pix.