Thank you all for your responses.
Arnie, no the plant isn't in a golden pot in the nursery. I was hoping the chart just had the wrong row or column shown for that plant. Seems that's the case.
I got my first two by just playing around and accidentally stumbled upon them. I wasn't keeping track or anything. But once I did find them, I focussed on growing and selling just those plants (since they give good prices) to build up my money. Then I could improve the nursery and get better supplies.
My first magic plant, which I won't name, but which sold by default for around $60, I managed to get up to about $150 and it still sells well. My second magic plant, which I also won't name, sold for around $270 by default. I've pushed that up much higher - between $600 and $700 and it only takes me 5-10 minutes to sell a nursery full of them. I actually priced that one at $800 once and sold one, but most visitors had frowny faces.
So if you're finding it slow going and you haven't tried this yet, you can experiment with prices on ALL your plants and try and get the funds to do a little more a little sooner.
Oh - I use a lot of supplies to boost the strength and flowers on all my plants too - I don't know that I'd get those prices for them if I didn't spend that bit of money at the start of each growing period...