That's a tricky question.
The short answer is, what ever someone is willing to pay. To determine this the best thing to do is to google, "scouts for sale" and see what people are asking, and more importantly what they are getting for scouts similar to yours. Hemmings is a good place to look as the asking price (what the seller/appraiser thinks it should bring) and the selling price (what the market will bear, that is what is willing to be paid) are both shown. We May not be the best audience to ask as most of us have waaay more into our trucks then what they are worth! Also be sure to check out the Scout for sale thread on this forum. They leave the sold truck threads up so you can look back and see trends. Very nice tool.
Here are some tips that might be helpful in determining the value of your Scout.
There are resources that collect and average this data for you like kelly blue book and the nada book, but they will vary from region to region, and will only give you an "average" price. Some trucks in such and such condition sold for 5k some for 15k average 10k.( not your truck, just an example) since so few scouts sell in any given area, at any given time, its difficult to get a accurate average. Now f150s on the other hand...
A rust free Scout like yours in michigan would be worth more than say, in California, where rust free is more common, but then again there isn't a lot of disposable income in that area . See how that works? But on the other hand, with the internet you reach people all over the country not just your area (I'm in afghanistan after all), so you have a much larger market.
That said, there are a few basic truisms when it comes to selling customized vehicles like yours:
1: labor is worth nothing, so what ever you have paid other people to do on your truck subtract that from the value. Your labor is worth even less.
2: you can not recoup the retail value of parts you put on your truck. I.e. A $5000 paint job does not make your truck worth $5000 more. A $8000 truck with a $5000 paint job is not worth $13000 unless someone is willing to pay that for it.
3: unless the buyer has the exact same taste as you, the modifications you make to your truck May turn off buyers. Paint color, rim selection, stereo equipment, all May have cost you money, but a potential buyer May not see any value in this if they plan to replace it with something that suits their taste. Case in point; I like the old rims better. The black out look is not popular in my area (or to my taste). On the other hand having the soft top is a plus in a warm climate. Do you have a hard top too? Limiting factor in cold climate.
4: auto vs manual. Stick shift will limit your buyers, especially in your area. I am one of only 5 people how can drive a standard transmission in my unit.
5: items such as "new" tires, brake lines, pads, clutch,wiper blades etc. Add little to no value to the resale, as buyers expect these items to be in serviceable condition when buying in this price point. (your truck is obviously not a thousand dollar clunker on billy bobs used car lot after all). This is not necessarily true form a "restorers" point of view how ever. These parts would have an impact on the quality of the restoration and therefore price.
There are more, but you get the point. Most people how build a [specialty] Truck for their personal use understand this and don't expect to get what they put into a vehicle out of it. Witness the average car add in the local auto trader. "1974 ( insert low collect-ability 70's car worth maybe $5000 in selling condition) over $20,000 invested, will sacrifice for $15,000. Add goes on to list thousands of dollars of parts and mods you don't want... Good luck!
I appraised vehicles for trade-in at a new car dealership for almost 10 years. Its very hard to do when you have the keys in your hands to test drive, a lift and shop full of certified mechanics and even harder online from a few pictures, form thousands of miles away.
With the info above, careful searches online and input form experts form here, you should be able to come up with a reliable value for your truck.
You don't say why you want to know. Are you selling it, insuring it or just trying not to over build it? These too are questions to answer when valuing a vehicle.
I hope this helps. Good looking truck!