All reputable HVAC Contractors offer free estimates to replace/upgrade your furnace, air conditioner, heat pump or ventilation systems. Please don’t confuse this with a service call to repair or clean your system. Most contractors are very flexible and willing to meet your schedule, including nights and weekends, to meet at your home for this estimate.
In most cases, the work is straightforward and the estimator is able to leave a written proposal prior to leaving. Be sure to get everything in writing and ask for brochures of the proposed equipment.
If you have further questions, the equipment manufacturers website is a great resource. Each manufacturer offers a number of options in their line so you will know if the good, better or best option is being proposed by the contractor. There is a wide range of options and prices so be sure you are getting an “apples to apples” comparison as you get your estimates.