Seems an awful lot to pay just to cut a hole in a wall doesn't it? But repairing a collapsed roof or wall would be lots more. And I don't think you can buy a coffin for 500. I assume that is fee for engineer? A "consulting carpenter", if you will allow, may charge less, but his recommendation may still be engineer or certified architect.
Heres an old joke, A repair man comes out to fix a washer. He takes a quick look, screws on a nut, hands over bill for $100. Customer is outraged, "$100 for one little nut?" "The nut was just 5 cents, $99.95 was for knowing where to put it."
Last night while tossing and turning in bed over this, trying to put it out of my mind by remembering 6 chicken enchiladas with green chiles I had for dinner, I thought of another area of concern. Well, same area just another concern. The wall may be part of a convoluted "rafter/collar tie" system to prevent walls, especially addition wall, from spreading. Addition ceiling joists are rafter ties fastened to top of wall. To prevent wall from being pulled over, it was fastened to short rafters, which are fastened to longer partners with original rafter collars. ( Wall could even be hanging from short rafters instead of supporting them.)
If, I say if, that is case, verified by on site inspection, you might be able to extend joists to collar ties. The other concerns still remain; is wall bearing load of short rafters; are extended studs of wall bearing load of addition roof; is there adequate support below to support wall supporting any of those loads, or just load of ceiling joists, especially if you cut a hole in it. As i sed earlier, this could be tooth pick bridge type situation, where no one thing is critical, but entire structure, as it stands, is sharing the load. Crack one tooth pick and entire bridge collapses.
"dig some foam out, but it cost SO much" Just dig out tickness to get to wery top where new rafters are fastende to whatever, width of hole enough to get good look at how they attach and to what. From top of rafter to bottom, if rafter to rafter, about a fool away from junction back along each rafter, if to a ridge board a look at opposite side of it where new rafter joins. New rafter may be fastend to side of old rafter, a look at both sides of that. Once that's all looked at you can re-fill hole(s) with large cans of maximally expanding foam built up in layers, 'cause that stuff can actually raise the roof if you try to do it with one big squirt.
Pic in post 87. Just to keep my non-academic theorizing going here behind these poison ivy covered walls. If the hall walls were removed would that and "pink room" be one long room? Does room in 87 also have the short "floating" rafters? Does addition extend along side of room 87?
Speaking of raising roof, somebody was, I have abandoned dynamite idea. Instead use kegs of black powder, deeper boom, lots of black smoke, use extra long sputtering fuse, have loud ticking clock, dramatic minor key music on stereo. Call for pizza delivery so someone is rushing to scene. Just before fuse reaches keg, make new post; "Be sure to return to this thread for the exciting Episode 121, "Rafters of Hell," of our thrilling serial The Doorway to Bankruptcy.