Older cheap sets were often complete rubbish but my more recent purchases have proved surprisingly good, including a dirt cheap metric set from Lidl (apart from the M4 tap!)
A great deal depends on how often you use the set and the metals you thread. More expensive sets last much longer on difficult metals like Stainless, but cheap sets – provided they're sharp – deliver long service on Aluminium and Brass, and do reasonably well on mild-steel.
Because threading steel tends to blunt inexpensive taps and dies, I now keep two sets : one for ferrous, the other for non ferrous work. Both are supplemented by particular sizes and replacements most of which come from Tracy Tools, because they hit my 'value for money' bullseye. (They also sell tap-drills, which you also need.) Owning two sets plus add-ons might seem an extravagance: it's not. Part of the tool revolution is accepting that disposable tools are reasonable substitutes to heirloom quality in a hobby workshop. It is no longer 1955!
My advice is to buy a cheap set like one of these; don't fret about quality, just replace as needed. After using them for a while you will know whether or not you need something a little better.
Dave