What is a cost effective way to level match, for comparing different hifi components?

The only reason I can think of to do something like this is to learn to judge volume. Listen to some music, take your reading, play the next thing at a volume you think is the same, take another reading. When the readings match pretty close you have a good sense of volume. From that point on toss the stupid meter it will only distract you from what really matters which is learning to listen. 

Use a voltmeter you can't level match with a SPL meter. You also need to do the test blind other than that just pick whichever one you think sounds better and don't worry about.

You also need to do the test blind

Do you REALLY need to be blind to judge equipment? I don't see very well. Is THAT good enough? Or do I need to go blind completely in order to assess the sound characteristics? If so, I think I'd opt for just  keeping my old Dac and my vision....or what's left of it. Wow! I never knew it was so demanding to buy audio equipment.

OP strict level matching is essential. Lots of good tools to help with this that IMO should be part of the arsenal. Test tones, SPL meter, DMM, and an RTA with a calibrated microphone ( I use the Studio Six set of tools which run on an IPad )

As you probably already know, the ear brain likes louder and louder is just chasing your tail from a qualitative perspective, unless you can level match. My mentor (RIP) in this critical area and a real stickler for matching to .25 db or better was Roger Modjeski.

and there are measures for speech intelligibility, using a recording of a familiar voice ( instrument, acoustic space, etc ) can be an excellent touchstone- I use a Zoom H-6. There is of course a big and obvious difference between recognizing “ mom” and understanding what she is saying.