Of course it depends on the car. With old Mercedes oder BMW, spare parts supply is excellent - Mercedes for example guarantees that they can provide any part you need (that means chassis, propulsion, safety - obviously they can't stock every interior part in every colour) for any car built after the second world war. And if they don't have it in stock, they'll make it. Of course, this has a price, but you need not worry. BMW is similar. And Volvo and Saab, which have a not-so-good manufacturer support have a "cult" following on the net, so you still get get nearly anything you need. And with BMW and Mercedes, the internet community and the car clubs also offer a lot of help, so in many cases you even don't need thge manufacturer.
For every car I ever owned I knew I would be able to find a (used) engine or transmission for under 500€ within a few days.
I do not know, however, if this also applies to a (US) Ford escort. For euro Escorts (entirely different car), most certainly it doesn't. They were crap when new, they are crap now. There were a lot of them, and they are ugly, so nobody cares about them...
Plus, somewhen in the late 80s, Ford's spare parts depot burned down, so spares just don't exist, and as everybody hates the car, there are no enthusiast who could help out.
That is one of the cars I'd never buy in the first place.
In your case, I'd start scanning the market. If you have the garage, perhaps even get a cheap, somewhat working beater and store it "just in case". Not much money tied up, but you know it is there (and working). Then drive the escort until it falls apart. If it does, take the beater and you have have all the time in the world to find a long-term solution. No need to rush and overspend.
(Ok, admittedly, I'd do it even differently. I'd just borrow a car from a friend - we have a kind of emergency mobility network: there are more cars than people, and not everybody needs his car permanently, so there are redundancies. For example, at the moment I drive a friend's Saab, as mine is in the workshop for extensive troubleshooting. Last year, another of my friends drove mine. If you know each other well and know you have the same opinions on how a car deserves to be treated, this works quite well.)