Scotchleaf,
Glad you were able to post more photos.
Here are my thoughts / recommendations:
First, I would think the gentleman who evaluated it for you was pretty close in his valuation. What you may have misunderstood is that he likely meant $800 as is. Along with the koshirae, the sword polished could be worth more in the range of $2000. Please note that is as long there are no unseen flaws. Possibly more depending on if it is signed, by whom and if it is shoshin.
The fittings look to be fairly decent. The kashira judging by the wrap, I would bet is horn. The fuchi is shakudo and the menuki look to be shakudo with gold highlights. The tsuba i can only tell is iron, but would like to see a photo of it.
Did the gentleman remove the tsuka to see if it was signed ? If so, was it and do you remember the name ? If not signed was the sword ubu or original ? If you do not know, please remove the tsuka and post a photo of both sides. While you are at it, a photo of the other side of the blade along with a photo of the tsuba and menuki would be helpful.
From what I can see the sword doesn't look beyond repair and depending on how you look at it, worth the cost of polish. Of course keep in mind that I have only seen photos and only of one side. An "in hand" evaluation by a polisher would be a must, as only so much can be derived from your photos. The polisher will be able to ascertain your best course of action.
Think of it like this, you have nothing in it. I'm guessing from the photos that the nagasa is approximately 18-20" in length. Let's say you spend $1000-$1200 on a polish, $350 for new shirasaya ( an option is to sell the fittings to cover the cost of shirasaya). You have a nice polished blade for less than what it is worth.
The key in your situation is that you inherited it. Where people get upside down on these things is when they pay too much in the beginning and then opt for polish, shirasaya, habaki, papers etc., etc.
Only my opinion, and worth every bit of what you paid for it.