That's crazy. I already updated the second floor, which is roughly 1400 square feet, 4 bedroom, 2 bathroom, stairwell for roughly 40k. Thankfully, my brother is a plumber and I can lay tile like fuckin picasso so the labor expenses were beer and $2k I stuffed into my brother's glove box so he couldn't refuse it. I painted, trimmed, installed new stair railings and updated the electric fixtures. I had someone install the hardwood and they charged me $2.50/foot, which is a bargain.
I'd do the same thing in the first floor, dump the house and build a new one before I spent 150/foot and the buyer can deal with the limited space in the kitchen.
The entire purpose of the addition is to add space to the kitchen, use a portion of the existing kitchen to build a mudroom off the garage and have my laundry on the main floor. If I go that route, I would need an architect/engineer b/c I'm opening up the back of the house, roughly a 30 foot span, and transfer the weight to the existing foundation. I know it won't be cheap to recess a beam to support that type of span and I'm more than happy to pay for this type of work. $8k to tell me where to put my toilet isn't going to happen, though.
I would build the addition on a crawl space with insulated concrete forms over a slab. I don't want that cold addition feel and need to run my heat and plumbing through the space so I think it's the best option. I worked with the forms before and it was easy and a great insulator, imo.