My opinion:

You should relax a bit and see if the "tech" will eventually return your call. Friday, weekend, Holidays, ........ the schedule can get a bit tight and I don't blame the tech for not wanting to do his day job on the weekend.

As for the price - seems a bit steep but I don't know the surrounding circumstances. Distance, hours spent, parts required and customer attitude can play into the pricing scheme.

Maybe try calling and leaving one more polite message?
Most of us service guys are really pretty nice folks. Likely to give you the shirt off of my back if you are desperate. Sometimes it feels like I'm running a charitable enterprise. Just be cool for awhile and see what happens.

We service folks get beaten up on every job.
Every person for whom I work must think that I've got some exorbitant profit margin from which I can instantly produce discounts in the form of free work, free parts, free diagnostics (I get the "free estimate" calls all the damn time.........sheesh). '... Would you please drive to my house, diagnose my problem, tell me what that problem is, give me an "estimate" for repairs, and then I'll make a decision. And while you're here, I need you to be certified, licensed, bonded, insured.........'

I'm also a customer - and I respect your opinion in the original post. I suspect that the original service tech may also understand your position indicated by his calling the seller in this deal in order to compare notes. If you keep your cool, all is not lost.

Just trying to help you see things from the service side. We're leery of taking another fleecing - especially this close to winter.