It's been said before on this Forum, several times actually, but unless you have absolutely NIL taps and dies, perhaps buying a full set is not the best way to go. Unless from a tip-top manufacturer (i.e. expensive) you probably won't get all 3 taps (taper or 1st, 2nd, & bottoming - there are other terms), AND you'll also often end up with probably a couple of sizes that you'll never use.
When I "changed systems" (moving here 30 years ago) and needed virtually all new Metric, I bought a set. But since then I've simply added to the odds n sods I inherited from my dad and already had, then adding the odd tap or die when they came up for "end of line" etc sales at shops, car boot sales (I don't go regularly), or from friends etc who've said "this might come in handy mate". These days you can of course add the bay, + local paper ads etc with job lots of people giving up, retiring, etc.
And don't forget those cheapo sets you see at Aldi, etc. Yes, they may all be made of cheese (they're not all made that way actually), but to have a cheapo set so you can deal with the odd one off thread that crops up and don't mind loosing is also a very useful back up.
Just my "cheap skate" approach, but HTH.
Only thing is, if buying odd one offs, make sure you store them safely, NOT just rattling around in a baccie tin! (I use lengths of model aero silicon fuel tubing and exhaust piping, etc, cut off to length. THEN they can go into the tin!)
AES