I came across a craigslist deal where a guy was offloading his NDK Greenlander that mostly floats (has a small leak somewhere - ha...) and in need of major TLC for less than 100 bucks ;-)

I would not pay $100 for this boat. It is essentially totaled and will require a huge amount of work to return to good condition. If you are looking for a boat project you will have more fun building a new boat from scratch. A new build would give you a better boat when you are done.

For every area of damage that you can see you must assume there are large areas of compromised structure around it. The construction is evidently primarily chop strand matt which has a very high resin ratio and is therefore brittle. If it received enough impact to crack in one spot, the area surrounding that spot is also degraded.

Unless you really want a large fiberglassing project, look for a cheap boat elsewhere. This one will not be cheap. Plan on at least a full day in a tyvek suit wearing a very good dust mask while using a right angle grinder to remove all the surface damage. Keep on grinding around the damage until you get to solid material. You will be able to see the difference between damaged and solid as you grind. The damaged will grind rough and crackled and the solid will grind smooth. Feather the area around the damage to create a smooth transition. Grind almost all the way through the damaged glass, leaving just enough to support your repair material.

With the amount of evident damage you will likely need to work in stages as the grinding will likely create a shell that will not hold its own weight. So one day you will grind sand and repair one section, let your repairs cure, then the next day you can attack the next section.

The repair will likely need to be at least 4 layers of 6 ounce fiberglass. Cut the patches in staggered sizes with the first layer being the biggest, the last being the smallest to match the feathered edges of the grinding.

After you have applied all your repairs, it will need a heavy sanding to make it smooth. You can then add fairing compound and or fill coats to make an even surface which you can then prime and paint.

If you are experienced and skilled, you can figure on a week of work, but it is probably more. Personally, I think it would would be more satisfying and fun to take 10 minutes with a Sawzall to cut it up and throw it in the dumpster.