That depends on if you are planning to cut it yourself, or have someone else do it. Stumpage value should run about 30-50% of the mill delivered pricefor the wood, depending on quality and product. Location is another consideration, as the bare land value price should include other assets such as water frontage, development potential, proximaty to services, accessibilty, etc. Also the distance to where you sell your wood is a factor, as trucking costs can eat into your profits.
If you're looking for someone to help you with your down payment talk to a logging contractor; he may be willing to purchase some or all of the stumpage. That is a double edged sword, however; once you accept his money it'll be a lot harder to kick him off if he doesn't abide by the cutting specs laid out in the contract you sign with him.
Having said that, many of the logging contractors here are buying former industrial land, recover their money cutting it, then either sell or sit on it and let it grow back, much the way the former landowners did for the last 2 centuries.
On a smaller note I purchased my lot 5 years ago for 10K; although it was cut hard in 1979, by the end of the summer I will have recovered that price from the overmature and dying trees I've cut. When I'm done my 20 acres will be healthier than when I started; and 7-10 years from now I'll need to do it again. I also left enough hemlock and spruce to saw for my garage and other building purposes; and although I've taken about 15 cords of firewood, and there is more remaining than I'll ever use.
Remember, that doesn't cover the cost of operating my tractor, saw, or other expenses.
The worst timber "stand" which I own is the 5 acres they didn't get into last time; I'm cutting the dead and dying beech in a way to promote healthier regeneration; but that is the only area which I'll never cut again.