SandShark
If you search Google, you can find plenty of places to buy equipment. Here's a link to just one such place.

John
If you can get installion for free, then you can probably get your installer, if they're licensed, to just go in and buy a new system at wholesale. If that isn't possible, then I would wonder at the ability of the person doing the installation as Freon work and wiring will be necessary to ensure a good installation. Johnstone Supply will sell you a system at normal retail and ship to your location, since they're in most states you would have to pay taxes too. www.johnstonesupply.com Something else to consider will be a gas or electric system. Which do you want? An electric system will be safer to use and install if your electrical service can handle a 70vac breaker/load, however gas is more pleasant to use and own but is more dangerous to own. When I retired as a contractor in '07' I could buy an inside electrical furnace with A Coil for, my cost for a 50,000BTU unit, @$500 including tax. An outside 36,000BTU Conventional Condensing unit was @$450 and a new thermostat was $25-$70, depending on type. I never sold a Heat Pump due to the extra initial expense and the future repair costs. This negated any operating savings if PC board repairs were necessary during the first 5 years. They usually were. Today't EER rating will be higher than the standard in '06' and so will the wholesale cost, but if your installer can buy using a companies/individual contractor license number, they can buy yours for wholesale. If you want to spec your own unit you can use this rule of thumb to get an idea of your heat/cooling needs. For heat use 4BTU per sq. ft. of floor space and 1 ton, 12,000BTU of A/C per 1,000 sq. ft. of floor space. At the most you can add 1/2 ton of heat or a/c to your own estimate for extremely cold or hot conditions. John