Hey Matt,
Thanks for the ping on this, yes our Design-Build company specializes in these type of Urban Infill projects. Given the need for additional housing and lack of land in Denver ADU's are a great solutions for additional rental income, multi-generation living or home office. We've received a number of request for these type of projects this year and are currently working through several custom designs. In 2016 we hope to release an ADU home series with a set price and turnkey solution. At this point though if you have a specific project in mind I would be glad to have a chat and can review your project zoning requirements, design process, construction cost, rental rates, etc.. just ping me.
You can check out one of our current ADU projects at http://root-ad.com/portfolio_item/3105-w-25th/
My brother at FreemanConstructionLtd.com is also the area's leading installer for https://www.studio-shed.com/ which is different but is a similar prefab backyard office solution.
In terms of cost numbers I think @Bill S. is pretty close and correct in that each project is a bit different. Zoning Codes allowing ADU's are U-SU-A1, U-SU-A2*,U-TU-B, U-SU-B2*,U-TU-B2, U-SU-B1,U-TU-C, U-SU-C2*, U-SU-C1, U-RH-2.5, U-SU-E, U-SU-H1, U-RH-3A, U-RH-3A. The bulk plane, allowable square footage, and massing is a bit tricky and very site specific, so we always do an initial Feasibility Study with each client to cover this and the questions above before getting into design on these.
-Zeke
