Don't think of it as a call for a quote, think of it as an initial sales contact. An unsolicited inbound phone inquiry is about the strongest possible lead you can possibly get. The potential customer typically won't expect you to provide a full quote on the spot, but will expect to have a brief conversation and either a follow-up email with pricing details or a follow-up formal sales/demo call scheduled.
In terms of pricing/value, you should already have estimates of value for different customer sizes/use-cases and put together prices based on those estimates. On the call, it's your job to learn as much as you can about their problem so that you can determine how best to solve it with the products you offer and where it falls on your pricing scale.
Don't do on-prem unless they pay you a boat-load more and SaaS isn't an option they're willing to consider. It's way more of a headache.
NDAs are usually fine, but better to pay a lawyer a couple bucks to throw together one for you and try and use that one all the time rather than having to review a bunch of different ones coming from other companies.
Travel is case-by-case. Definitely not necessary for just a quote, and not strictly necessary for sales if your video demos/sales calls are on point, especially if your customers are tech-inclined.