Turning a SFH into a duplex- estimating cost

[Chelsea Mastin]

I hate to ask for help, but am having one heck of a time figuring out an estimated cost for renovation on a property I will be closing on at the end of the month. It's 1,344 finished single family manufactured house built 2005 over a 1,344 sqft basement with 9' ceilings (2,688 total sqft.) The pluming is roughly in as well as loads of building materials. The problem is that it is Aurora, CO- one block outside of Denver and all licensed contractors are booked out for months and charging what I consider outrageous prices per books/online estimates I've came across. 

The previous owner was passed away in beginning phases of turning it into a duplex; its is zoned R2. The city does not have any duplex related permits. I would like a separation of gas and electric, framing, dry wall and doors. I can then complete the rest myself and/or sub out the remaining work. I've contacted 9 licensed contractors and have only received two estimate of 30k-50k or 80k-100k for full reno. One said the pricing it's due to the height of the ceilings (9') and that since it's below manufactured home it will require "specialty" framing work. 

I would think that the materials, age or the property (2005) and rough pluming would save me quite a bit?? lol I'll get multiple itemized estimates after closing, but would like to get finances in order prior. Any insight?? These guys just taking me for a ride?

[Bill S.]

FYI it is my understanding that you can not do a "condo" for two units in Colorado. @Chelsea Mastin so your charge to contractors is a bit like. How much does it cost to build a house. The person that gave you the $30-$50k bid has no idea what they are doing. Years ago (~10) the going price for a basement finish started at $30 per sq ft. On top of that, you want to do separate systems (electric, gas, which means a furnace and water heater. To get real bids, you need a detailed written scope of work that includes finishes and a list of materials you will be supplying. It sounds like you are trying to do this on the cheap. To do so, you need way more knowledge than your post demonstrates. My advise would be to find a basement finish contractor and work with them. Also what you are proposing is not a "full reno" but more like a basement finish with some modifications. I would be floored if you could get the project done for less than $80k based on the picture.