I have the second commercial hatch as noted (links) above. Works ok and It did cost me some money just like the link states. If you are to poor to buy one of these, please think about use the whole removable floor as a work around (It won't cost any extra $$'s and you won't cut up your good floor hatch).
With a little care I can get my 15hp outboard down into the engine room through the commercial hatch. The hatch weighs about 30# +/- and is not to hard on the feet +/-. I painted it brown to look a little better. It is flush for the most part. It always has small amount of water in the hand hold dips except while sailing on rough seas. It gives fast access to the propshaft and aft end of the engine room, but it did cost real money. I know, I too wish everything was for free, and took no time. but some how it is combo of time and money.
The Plex or lexan hatches are not for this type of service! they are for up on deck service = low, or no traffic.
Norm
(edited 9/6/13) I forgot; I did add a little reinforcing rib (2"down) around in the floor hatch around the bottom of the mount ring on the commercial hatch, it also tied in the mounting bolts for the ring, without it (the reinforcement) the floor flexed a bit more than I liked. The hatch takes out allot of the floors ply core.
Chris (sorry I did indeed miss the word USED in your post) my links were for new, for used ? maybe look at some of the boat yards some times they strip old worn out work boats but the hatches may also be worn out. You may want to check at
Minnies they have some of almost everything.