If you aren't one of those people
(like me) that accumulates test equipment because it is cool, fun to repair, etc then let your need be driven by what you are doing on your bench. If you are doing a one off filter project, you probably don't need a vector network analyzer. If you do a lot of stuff where bandwidth and impedance matters, you probably do. Then the question becomes
what specs do you need to do the work you need to do?In the real world, price and performance are correlated. Thirty dollar TE won't ever match its three hundred or three thousand dollar equivalent. That said, cheap TE is often all we need. Take VNAs as an example.
There are sixty dollar VNAs out there that do a lot for the money, especially if you are working under 100MHz. They don't come with good documentation, are sometimes hard to use, and have real performance limitations. The next step up is kit that costs five to ten times as much and comes with better docs and performance. For example, the SDR-KITS WVNA works pretty well up to 1GHz, has a big community of users, and does a lot for the money. Then there's the pro gear which can cost a hundred times as much. The truth is, most of us never ever need a VNA that goes to 20GHz or a DMM with 8.5 digits. That doesn't mean we don't own such stuff but that's because either we
have to have it for a particular project or we
want to have it because damn owning a rack full of spectrum analyzer is cool.
So here's one strategy: start with the cheapest option you can find that probably does what you need. Again, if you need a VNA, do some googling, buy the sixty buck VNA, learn how to use it, and set it aside for something better when you need something better. Maybe you will work your way up to the Agilent or RS rack mount VNA, maybe not.
One other thing. Beside google being your friend, get to your bench and do shit with the stuff you buy. The only way to really understand anything more complicated than a voltmeter is to use it an awful lot. And, actually, you can probably say that about a VOM, too.