It's highly dependent on who you hire I have discovered, I have rehabbed with 'side-job' workers for a fraction of the price. Accurate prices are hard to come by because it depends on time of year and local factors. Give your investors a range depending on these factors and you'll be more believable.
I've had an entire house rewired for $1500 on a good day and $5000 on a bad day. You can make a spreadsheet with 'rule of thumb' costs for most things and use it to ballpark the figures. Contractors have these in their head already so you can find a local general contractor/builder to give you these numbers. Most contractors when they look at your job already know the ballpark per amount of material or room or whatever and are just deciding how much to tack on for degree of difficulty and how fancy your house looks. They know they'll lose money if they go below that so that is your 'bottom end'. If you need a permit that will be extra. if they have to fetch materials that is extra.
For example this is kind of my 'max I'll pay' for various things based on past experience. (and yes I'm sure others have gotten better deals).
Concrete: $75 a yard installed
Brick: $.50 per brick installed
painting: $100-150 a room with trim
exterior painting: $1800-$2500
new hvac : $2300
new window: $100-$150 for standard sizes x 2 for install
drywall : $12-$18 a sheet finished (depends on finish level and size of sheets)
tile: $5 a square foot installed (add material cost of between $2 and $10)
basic stainless appliance package : $2500
hardwood $2 a sq. foot installed $1 a sq foot to refinish (add material cost of $2 to $10)
plumbing: $100 per fixture to install and $100 per fixture rough-in
electrical: priced per outlet and per fixture for both rough-in and install
Total rewire of house: $3K-$6K
upgrade electrical service: $800
Total replumb of house with pex (no slab): $2K - $5K
10x10 set of cabinets no frills: $2500, about 1 day for a capenter to install
countertops: $1500-2000
new roof: $5K (metal including materials)
deck: $2K-$5K
bulldozer/bocat: $80 an hour
dumptruck: $1.50 per mile
Carpenter: $35 an hour low end + $10-$15 an hour for helpers. 2 carpenters can frame an entire house in less than a week. Trim 1-2 rooms per day.