I picked up the concertina a few years back at age 64 or so. I do play it decently but only have a couple of sets I can keep up with at a decent session. And boatloads of tunes I can play at a slower place that give me great joy. Heck I do love it. I got a Conner years before, before hybrids were a thing, but never did get a chance to give it any time for over 15 years. I was lucky enough to have that good sounding instrument to learn on. Then I lucked into one of the best concertinas made.
I think some of the hybrids are decent entry level instruments, and some are lifetime instruments. But even those are pricey. If you want to see, "Does my brain work this way" try renting something. The Button Box has some if you are in the US.
Concertina playing is sort of counter intuitive, sort of like touch typing, switching from hand to hand for melody lines.
If you don't have a concertina teacher around I recommend taking a few months of lessons on The Online Academy of Irish Music. They build up systematically.
There is also one more thing to consider with concertinas. There are Jeffries systems and Wheatstone systems. They are basically the same on two rows, but the accidental keys on the top (third) row, including the very important C# are in different places. I play Wheatstone system, but lots of people play Jeffries system. I do believe that the Jeffiries systems are most popular. But I'm not sure.
As for the button accordion, I do wonder with the smaller lighter instruments out there now if I would have been tempted if they were available at the time I started. Some swear they are easier to learn. I have no idea.
And you are right on the prices. The best whistle you can get your hands on by a living maker is a drop in the bucket compared to the price of an excellent concertina.
Though in Ireland there is a company called The Irish Concertina Company that is making concertina reeded models that are relatively quick to purchase. I have never had personal experience with one of them. Modern makers of concertina reeded models have relatively to extremely long waiting lists.
Hybrid models are less expensive and vary in quality of action and sound.
There is a forum out there concertina.net similar to Chiff and Fipple. Join and ask questions.

Oh yeah, I play flute, whistle and concertina out in the world, and fiddle at home every day as well.