I have a 30X80 Optolyth, it isn't for sale but I bought it recently and so did some research.
Glasgow Binocular Repair Centre will give an Optolyth a full clean, service and line up for about £70 including return postage, so in theory it should come back good as new. This alone makes them a good buy as mine is a little dirty and so does need a clean, as will most draw scopes of this age.
The other thing worth considering is how you will steady it when using it in the field, this is probably the single biggest factor in using a high magnification scope especially if, like me, you've no intention of carrying a tripod. I've found it is best to lie down with your back against a bank or peat hag and rest the scope on your knee. However, the longer the scope the easier this is to do which is why I went for the 30X80 Optolyth which is a 2 draw scope whereas the smaller objective scopes are only a single draw and so are shorter and I've no idea how you might support one of those unless you were to lie down and rest it on a rucksack of heather clump.
The S&B spotting scopes look like exactly the same scope as the Nickel Supra. The Nickel scopes come up on ebay and such places quite often for between £50 and £150. It might be worth checking if the Glasgow Bino Repair people would service one of those, and the cost, as well as that might be a major factor in deciding if it was a good buy. I believe Nickel will still service them. For a while there were 3 or 4 on ebay all the time but at present there seem to be very few spotting scopes, no idea why, but they are out there and I'm sure the numbers will increase in due course.
The Gray's scopes are very long and so ideal for spotting in the field but they also still do big money, even second hand.
Another thing to bear in mind is that big magnification spotting scopes are, for the most part, a full daylight proposition for spotting deer.
In your position I'd guess that the 30X80 Optolyth or the Nickel Supra would probably be your best bet unless you want to spend big cash. For what it is worth I've been enjoying using mine and have got some fun out of it and amazed a friend by taking him out onto some moorland where I thought there might be some sika stags feeding and letting him watch a big 8 point stag at 750 yards with the spotting scope. Pure luck, of course, but he thought I had some sort of magic insight into the movement of the big stag to be able to find him like that