Yeah, the Sekonic L358 sort of became "the meter" for hobbyists...kind of the way Minolta AutoMeter III-F was the big hobbyist model back in the mid-1980's. Sekonic really took over the business that Minolta and Gossen had come to dominate, and Sekonic still has the current lead in popularity. The older Minolta AutoMeter III-F was a so-called combination meter, meaning a light meter that was capable of reading ambient light, but also capable of taking flash readings, in a fairly simple manner. A true flash meter on the other hand offers more functions, like automatic multi-pop calibration, corded operation, not just cordless, percentage of flash-to-ambient readouts, stuff like that. That's why Minolta had the Auto Meter line AND the Minolta Flash Meter III and IV line.
WHy are these things not cheap? I would say high-quality build and designed to LAST, slow replacement cycle meaning few sales opps for upgraders/replacements, and also high utility. A GOOD flash meter can last two to three decades. I bought a Minolta in 1986...still works great...so...no "new unit" sales for Minolta...anyway...a LOT of them are also bought and not used and are sold, so look for a good, clean used one. Since digital came onto the scene, the absolute, utter, total NEED for a flash meter has been cut down by about 95%. Which I think has further reduced the SALES opportunities for the manufacturers of flash meters, so they keep prices high.