Yep, the cost is in the trip is a big factor but sounds like it was their choice to try to sell you. You did the right thing by asking them do the calcs before they came out. Millions of questions are time consuming and costly but better than someone rushing into and pausing mid project with in-decision.

We (I'm cofounder of Electric Air, HVAC contract) have had people pause on day one of install, and that ends up costing the company $10-20K due to delays. Mostly because there isn't something for the team to do for that day or two while we scramble to line up the next customer.