Such things aren't always about "monetary value." The Tech I's (and Tech II's) are fantastically awesome knives. The handle material is really nice. The balance is really nice. The looks are really nice. The steel is really nice. I have 1 of each and they are on my never-ever sell list.
My very opinionated opinion: do the deal. If you need to think "cost" then amortize a daily cost over the next 30 years. Up-front cost may seem steep, but if you think daily cost, then the buy-it decision is easy.
I'll pontificate a little, philosophically speaking, from my user's standpoint. Some knives are rare and worth the money. I got lucky today on a 'bay thing and scored an old Western 8"-blade-length fighting knife. Surprisingly good shape for the price paid. The leather sheath is really old, not original, barely serviceable to keep fingers off of sharp edge. All in all, I couldn't care about the sheath. The Western itself is a relatively rare "timeless classic" knife and I was lucky to get it.
I feel the same way about the SOG Tech I (and Tech II). Nuts to sheath or box, they don't cut, they are simply a hanger-on ..... if you can score a real-deal Tech I knife at a price you are willing to pay, or even a few bucks beyond your price pain threshold, I'd say do the deal.
A while back I bought either a Tech I or a Tech II, without sheath, and I was thrilled to even find one, and twice as thrilled it was affordable and not priced way beyond my price pain threshold. And a short while after that I lucked into a genuine SOG sheath to fit the knife. Patience and luck sometimes gets you where you want to be.
Cheers,
Carl