I buy inexpensive lines for most of my fishing because they get abused a good bit. I shore fish a lot, and it's common for the line to lay on bare dirt & rocks and inevitably get stepped on a few times, twisted around shoreline weeds & brush, and the cheap (eBay) lines seem to last as long as the high dollar lines under those conditions.
I will fish a line until I see/feel damage (cuts or nicks in the finish most common), then switch to a new line. Some of them last a year or more, and a few have been replaced after one trip.
Not the line's fault in most cases, just that it got rough treatment.
As for actual performance, I can see little difference in a $10 line compared to a $75 line under the conditions where I use them 99% of the time.
One of the worst lines I ever tried was a $75 line which had a factory defect (twisted core) and was quickly replaced by the manufacturer. The replacement was defective, too (blemish in the coating).
It was again replaced by the manufacturer, but at that point I had more money in postage to return the defective lines than I would have had in an eBay line I usually buy.