Is it worth paying a high price for sa supposed quality plg or can
equally used the much cheaper ones?

Been QRT for over 25 years and should be on the air in a few weeks
with a FlexRadio 6300

The cheap ones tend to be nickel-plated brass. They can be a bear to
solder (it doesn't "wet" nickel easily) unless you grind off the
nickel to expose the brass. The cheap ones also tend to use
poorer-grade insulation such as nylon, which doesn't stand up to
high-heat soldering well... and since you need to apply a lot of heat
to these things to solder them, that's a problem. And, I've seen
cheapies whose thread dimensions seemed to be a bit "off" or which had
some roughness in the thread or barrel, and didn't fasten into the
socket smoothly.

The really good ones are silver-plated, and take solder much more
easily. They also use Teflon insulation, which resists soldering heat
quite well.

"Cheap is often very expensive". It's frustrating to have to go
through two or three cheap connectors, several installation attempts,
and a "Damn it, there's an internal short, gotta cut it off and try
again" which ends up costing you lots of time, and (sometimes) more $$
on connectors than if you'd just gone ahead and bought a good one to
start. And, having your rig not work well (or even suffer high-SWR
damage) because your connector wasn't *really* soldered right, and
went "open" or shorted out at the top end of the feedline right in the
middle of a contest or new DX contact... well, "imagine the grousing"
as my wife puts it.

HRO carries silver/teflon PL-259s for $2.69, Quicksilver sells 'em
4/$12 (or 4/$10 for the crimp-on style), and other mail-order dealers
probably have comparable prices. "Saving" a buck or so buying a cheap
connector is really not worth the risk of hassle.