Perhaps a bit noisy but, not if you have insulation under them (when installed). :)  Keep in mind, that YES they are more expensive AND, they may actually get small "dimples" in them from hail... it will show (in many not all) forms of metal roofs but that is NOT covered by insurance (cosmetic damage). 

I think the smaller 2-3 bedroom STR's are a little bit insulated though there are some large condo projects going on as well. 

The renovation process may involve updating the interior and exterior of the home, replacing outdated fixtures and appliances, improving insulation and energy efficiency, as well as meeting safety and code requirements.

Choosing the most expensive insulation because it's the most energy efficient, should allow you to reduce and/or eliminate costs in other areas.4 - Energy efficiency isn't made up of added costs.5 - Energy efficiency is the product of reducing energy needs, not supplying added energy.6 - Cost effectiveness is a product of maximum use of materials, as in little or no waste.All of the above should be obvious, in parts. 

They can buy and install windows/insulation/cabinets/etc for less than you can buy them for....

Insulation?

Are there ways to improving the sound through foam insulation in existing walls?

It makes it very easy to find customers even with bad support.I am leaning towards going with the click plank option as I was told, that when it clicks together it adds another substrate or "floor" basically and that with the attached underlayment does a pretty good job of reducing noise.I looked at adding gypsum concrete (gypcrete), self leveling cementitious subfloors, wool insulation under the plywood, and another type of cement type floor, but they all have their pros and cons and doesn't seem to be worth the extra money in the end. 

If your shell is back to the studs, just getting the rough in phase; insulation mechanical, duct work, electrical, plumbing passed inspection, with the holding costs that will put you over 100k.  

Even the correct insulation matters.