Bill:
These blades/any blade will ring or sing clearly if there is no cracks. The tone can be a telling note - if it is dull then the blade has issues (maybe a hairline somewhere), if it is clear then the blade is solid. I usually check with a flick of my finger or lightly tap with a quarter. For a cross cut blade I like pretty aggressive set on the blade. Most saw blades are set around 5 degrees or so. The family has always set a more aggressive angle somewhere about 7 to 10 degrees of set to either side - makes for a wider kerf but a safer cut. You also need to see the blade cleaned. Check on the formation of the gullets as well. Malformed gullets will cause serious over heating issues and damage the blade. In the gullets is where you will see any possible cracking. Look for aged on build up of pitch and debris as well as chips in the teeth. If there is build up you will have to scrape the build up off (a pen knife works well) to see if there are any hairline cracks. If there are
ANY cracks at all - walk better yet run from the blade. Buying a cracked blade is an emergency room or a morgue visit waiting to happen. Most cracks in the blade can be stopped by drilling stop holes - but that really should only be done by a pro sharpener, one who
really knows what he is doing.
If you think the blade is worthwhile then the value comes into play. I bought 4 blades 3 years ago - 3 - 27" blades and a 25" blade. I paid $60.00 for them. Clean blades (oxidized of course) good gullets, rake/hook angles look good, just need some sharpening and a re-set.
I intend to take all of these blades to my local pro saw shop and have them all tuned up. Even though I have sharpened blades for over 40 years, I am not a pro sharpener. I redid my own blade that is currently on my saw table this past September. I normally use a flat bastard file but this time I wanted to rebuild the gullets and set the hook properly so I used my 4-1/2" grinder (worked like a charm). What normally takes about 40 minutes by hand I did in about 15. Man did that improve the cut

After the other blades are done up by my local pro my current blade will go the same route.
Oh yeah ... if the blade is on an arbor, check it for true in round. Take a pencil and lay it in front of the blade. Slowly rotate the blade and see how many teeth will just contact the pencil when the pencil is pushed into the front of the blade. If more than a few miss - the blade will have to be trued back into round and then reground.
I wouldn't pay much more than $25.00 or $30.00 for a good 27" blade that has been sitting a while. Make sure that it hasn't been hanging outside on a barn wall or something. If it has stay away from it - probably warped.
I did a search on

- seems most of these blades are marketed toward the arts and crafty folks - wanna paint a blade

But there are a few hits - mostly for 21" and below, mostly in the $39.00 range. There was one hit for a larger blade with a larger price.
Large Sawmill Buzz Saw Blade 30-1/2" Diameter Solid Sawblade