Don't know where you are but out here on the "left coast", California, these old Honda's go for a premium because they are such good stuff. Especially the longshafts for sailboat kickers.
It is too bad though that many are left to rot the lower end in salt water on the backs of these boats. Because, case extensions and gear boxes from suppliers like boats.net are cost prohibitive to replace.
But, if you can pull it out and see if it will clean up, you can do some reliable patching with fiberglass cloth or even epoxy and Bondo for just pitting. As long as the housing is sound and can accept new seals, it can be repaired and put back in service. The internals don't cost too much to resurrect one and if an older one has parts listed as "unavailable" or "obsolete" they can often be found on some of the 1990's parts lists. The ignition coils come to mind as an example.
One in decent mechanical and cosmetic shape, out here, can fetch upwards of $700 which is less that 1/2 price from a new 4 or 5 hp from Mercury or Honda or...? And, there are quite a few for sale each month if you live in SoCal and are willing to take a drive to pick one up.
I also see them being sold in pieces on ebay from time to time and the housing parts can be fairly reasonable if you jump in and bid.
They are pretty easy to work on but get the HelmInc. shop manual if you decide to do the work. Around $30
Here's the page to start looking
http://www.boats.net/parts/search/Honda/Outboard Engine/0/parts.html
Your motor will be listed under the 75HP banner as they screwed this page up and refuse to fix it. I don't see your serial number but maybe HONDADUDE will see this and help you figure it out exactly.
Bottom line? if you worked on bikes and can do a compression test, are proficient using a multimeter and know what PB BLASTER is, you can work on these no problem. Just get the shop manual and clear off some bench space. If not, I buy old, not running Hondas to turn 'em around and put 'em back out there. As do many other guys that get there before me!
Good luck and welcome to the forum.