You go to the gas station and instead of listing the price, they ask you to bid for the gas, would you?

The CO would be gases that are unwanted mostly. basically every heating appliance that "burns" gas will cause CO.

Utilities costs tend to be electric, cable, internet, and possibly propane/gas, water, and sewer but depends on the property.  

@Christopher Ball I am located in CT also and if it were my primary residence and natural gas was not available I would go with a forced air propane system.

Natural gas to heat up a 2000SF home at 69F is about $650/month, easy.

Annual property taxes are $1,961 ($163/month) and the building owner pays the following average utilities: water/sewer $55/month, electric $90/month, natural gas $90/month, insurance $135/month.

I have had the same thought but the truth is, do you earn points and rewards when you pay your gas bill or mortgage or taxes?

(install a cap cover for the gas furnace flue on the roof)The PM has it is on HVAC guy, that asks for 425$, but it sounds a bit expensive.Recommendation for a great HVAC in the area (KS MO 64138), also will be highly appreciated! 

Does anyone know of a general contractor in Gwinnett County that will accept <$100 or gas $$ and a referral?

In general, there are three options on most mobile homes: 1) central gas unit 2) central electric unit and 3) electric window heat/air.