I’m basing my estimate off the process of Ho-Oh and the 3 legendary dogs. Most of those are going for over $1000. I would put houndoom for $750.
me personally… I wouldn’t let mine go for less than around 750. tho it’s not for sale haha 
I just got one of these beauties back from PSA.
Just checked on eBay and the last one finished at auction for 935$ usd. $$$$$$
www.ebay.com/itm/2001-Pokemon-1st-Edition-Houndoom-Holo-8-Neo-Revelation-PSA-10-GEM-MINT/333236962188?hash=item4d9678838c:g:paAAAOSw9hddB6Wh
www.pokemonprice.com/CardDetails/a342b9db-729d-4a8b-9200-f493bf15281e/houndoom-holo-1st-edition
As @ptothestothea said, the last one was $935 with 31 bids, 17 unique bidders and 3 of them over $900. It’s a pop 26 card and doesn’t come up that often, $750 would be the low end of the price range but there aren’t really enough data points to develop a good range.
$750 mentioned post was from 2017
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Wow necro, I didn’t even notice … locking