Ohh man. That's a bummer but at least you know what you're getting in to. Depending on what roof you put on it'll be 20-25k on the lower end.. at least here in San Diego.I 'd bring a demo crew in to strip it and then let the roofers have it from there. I don't ever hear about people recycling shingle roofs but then again I hardly run into them anymore. Might be worth putting a feeler out and see if someone will come strip it for the wood!!
If you do end up wanting to do a fumigation, do it after every last piece of new wood is in that house, including cabinets. New lumber these days is full of wood pests now, they don't kiln dry them anymore.
Sounds like a fun project, I would take a house like that any day of the week for the right price. I inspect so many flipper houses and know that they're going to be doing major repairs in the next 5 years. Lipstick on a pig is an understatement on some of these things.
Get'er done!!