There are three different and only broadly related values antiques people would use, and all of them get used without clear distinction on Antiques Roadshow type programs:
Insurance value - this can really be anything you want it to be, as long as the insurer accepts the cover and you can keep up payments. It should reflect the cost to you of loss, which is usually taken as buying a replacement for your antique Georgian DVD player, which may or may not be easy in itself, and associated expenses and costs, plus covering any emotional loss you may felt.
Retail or sale value - what an antique shop or dealer would sell it for. Their cost for buying something plus their margins. This is usually determined by keeping the price low to get it out the door quickly, because the alternative is that it sits there wasting space for 15 years before a broken tap floods your store and ruins it.
Buying price - what they would pay somebody who turns up at their shop wanting to sell their genuine piece of French provincial tat. Ideally zero, but something like a third to half of sale price.
Auction price can be unpredictable, and two cashed-up idiots can break records by losing control of their bidding, but someone smart should be trying to get out before they reach retail buying price, or otherwise why bother with the auction at all.
For an item that is not in good condition, potential restoration costs will figure into each of these calculations but all three types of pricing are strongly influenced by other factors than your X and Y.
A bad restoration will actually drop the price, especially when your art gallery employs Spanish cleaning ladies to help. Plus,n ot everyone wants to do restoration either. As someone who does buy this stuff I prefer paying for the original object and its patina and character of authentic age, rather than paying for a restoration that has possibly altered its appearance and lost authenticity, which you never get back once its gone.
I’m not sure how widely its been shown but there is an excellent British tv series ‘The Repair Shop’ which looks at how high quality conservation and restoration is done. In many cases there is a trade-off between the cost of the object, the sentimental value, cost of restoration and loss of authenticity.